doc: update links in contribute.html

CLA links are now redirects. Use new URLs instead.

Also, use https:// links for all Google sites where
the http version just redirects to https anyway.
(That's all links on the page, as it turns out)

LGTM=adg
R=golang-codereviews, adg
CC=golang-codereviews
https://golang.org/cl/69980051

doc/contribute.html

@@ -22,7 +22,7 @@ you're working on if you want it to become part of the main repository.
 
 <p>
 Before undertaking to write something new for the Go project, send
-mail to the <a href="http://groups.google.com/group/golang-nuts">mailing
+mail to the <a href="https://groups.google.com/group/golang-nuts">mailing
 list</a> to discuss what you plan to do.  This gives everyone a
 chance to validate the design, helps prevent duplication of effort,
 and ensures that the idea fits inside the goals for the language
@@ -135,7 +135,7 @@ are inside <code>$GOROOT</code> when issuing commands.
 Windows users may need to perform extra steps to get the code review 
 extension working. See the
 <a href="https://code.google.com/p/go-wiki/wiki/CodeReview">CodeReview page</a> 
-on the <a href="http://code.google.com/p/go-wiki/wiki">Go Wiki</a> for details.
+on the <a href="https://code.google.com/p/go-wiki/wiki">Go Wiki</a> for details.
 </p>
 
 <h3>Log in to the code review site.</h3>
@@ -146,7 +146,7 @@ The code review server uses a Google Account to authenticate.
 <a href="https://www.google.com/accounts/Login?hl=en&amp;continue=http://www.google.com/">sign in at google.com</a>,
 you can use it to sign in to the code review server.)
 The email address you use on the Code Review site
-will be recorded in the <a href="http://code.google.com/p/go/source/list">Mercurial change log</a>
+will be recorded in the <a href="https://code.google.com/p/go/source/list">Mercurial change log</a>
 and in the <a href="/CONTRIBUTORS"><code>CONTRIBUTORS</code></a> file.
 You can <a href="https://www.google.com/accounts/NewAccount">create a Google Account</a>
 associated with any address where you receive email.
@@ -165,7 +165,7 @@ Saving authentication cookies to /Users/rsc/.codereview_upload_cookies_coderevie
 
 <h3>Configure your account settings.</h3>
 
-<p>Edit your <a href="http://codereview.appspot.com/settings">code review settings</a>.
+<p>Edit your <a href="https://codereview.appspot.com/settings">code review settings</a>.
 Grab a nickname.
 Many people prefer to set the Context option to
 &ldquo;Whole file&rdquo; to see more context when reviewing changes.
@@ -240,7 +240,7 @@ These can be code review nicknames or arbitrary email addresses.
 Unless explicitly told otherwise, such as in the discussion leading
 up to sending in the change list, leave the reviewer field blank.
 This means that the
-<a href="http://groups.google.com/group/golang-codereviews">golang-codereviews@googlegroups.com</a>
+<a href="https://groups.google.com/group/golang-codereviews">golang-codereviews@googlegroups.com</a>
 mailing list will be used as the reviewer.
 </p>
 
@@ -286,11 +286,11 @@ Files:
 
 <p>
 The special sentence &ldquo;Fixes issue 159.&rdquo; associates
-the change with issue 159 in the <a href="http://code.google.com/p/go/issues/list">Go issue tracker</a>.
+the change with issue 159 in the <a href="https://code.google.com/p/go/issues/list">Go issue tracker</a>.
 When this change is eventually submitted, the issue
 tracker will automatically mark the issue as fixed.
 (These conventions are described in detail by the
-<a href="http://code.google.com/p/support/wiki/IssueTracker#Integration_with_version_control">Google Project Hosting Issue Tracker documentation</a>.)
+<a href="https://code.google.com/p/support/wiki/IssueTracker#Integration_with_version_control">Google Project Hosting Issue Tracker documentation</a>.)
 </p>
 
 <p>
@@ -302,7 +302,7 @@ which <code>hg change</code> will print, something like:
 </p>
 
 <pre>
-CL created: http://codereview.appspot.com/99999
+CL created: https://codereview.appspot.com/99999
 </pre>
 
 <h3>Adding or removing files from an existing change</h3>
@@ -601,7 +601,7 @@ local repository out of date; must sync before submit
 
 <p>Files in the Go repository don't list author names,
 both to avoid clutter and to avoid having to keep the lists up to date.
-Instead, your name will appear in the <a href="http://code.google.com/p/go/source/list">Mercurial change log</a>
+Instead, your name will appear in the <a href="https://code.google.com/p/go/source/list">Mercurial change log</a>
 and in the <a href="/CONTRIBUTORS"><code>CONTRIBUTORS</code></a> file
 and perhaps the <a href="/AUTHORS"><code>AUTHORS</code></a> file.
 </p>
@@ -616,13 +616,15 @@ In order for them to do that, you need to have completed one of the
 contributor license agreements:
 <ul>
 <li>
-If you are the copyright holder, you will need to agree to
-the <a href="http://code.google.com/legal/individual-cla-v1.0.html">individual
+If you are the copyright holder, you will need to agree to the
+<a href="https://developers.google.com/open-source/cla/individual">individual
 contributor license agreement</a>, which can be completed online.
 </li>
 <li>
 If your organization is the copyright holder, the organization
-will need to agree to the <a href="http://code.google.com/legal/corporate-cla-v1.0.html">corporate contributor license agreement</a>.
+will need to agree to the
+<a href="https://developers.google.com/open-source/cla/corporate">corporate
+contributor license agreement</a>.
 (If the copyright holder for your code has already completed the
 agreement in connection with another Google open source project,
 it does not need to be completed again.)