doc: remove the confusing use of CL

CL (change list) pops out of nowhere and confuses the
reader. Use "change" instead to be consistent with the
rest of the document.

Fixes #18989.

Change-Id: I525a63a195dc6bb992c8ad0f10c2f2e1b2b952df
Reviewed-on: https://go-review.googlesource.com/36564Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/contribute.html

@@ -466,7 +466,7 @@ changes to Gerrit using <code>git</code> <code>push</code> <code>origin</code>
 
 <p>
 If your change relates to an open issue, please add a comment to the issue
-announcing your proposed fix, including a link to your CL.
+announcing your proposed fix, including a link to your change.
 </p>
 
 <p>