doc: fix bad lib/time link in 1.12 release notes

There's a "lib/time" sub-section in the Go 1.12 relase notes that
points to a non-existent golang.org/pkg/lib/time page.

The note is about a change in the tz database in the src/lib/time
directory, but the section's title (and the link) should probably just
refer to the time package.

Change-Id: Ibf9dacd710e72886f14ad0b7415fea1e8d25b83a
Reviewed-on: https://go-review.googlesource.com/c/164977Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.12.html

@@ -611,17 +611,6 @@ for {
 
 </dl><!-- io -->
 
-<dl id="lib/time"><dt><a href="/pkg/lib/time/">lib/time</a></dt>
-  <dd>
-    <p><!-- CL 151299 -->
-      The time zone database in <code>$GOROOT/lib/time/zoneinfo.zip</code>
-      has been updated to version 2018i. Note that this ZIP file is
-      only used if a time zone database is not provided by the operating
-      system.
-    </p>
-
-</dl><!-- lib/time -->
-
 <dl id="math"><dt><a href="/pkg/math/">math</a></dt>
   <dd>
     <p><!-- CL 153059 -->
@@ -935,6 +924,17 @@ for {
     </p>
 </dl><!-- text/template -->
 
+<dl id="time"><dt><a href="/pkg/time/">time</a></dt>
+  <dd>
+    <p><!-- CL 151299 -->
+      The time zone database in <code>$GOROOT/lib/time/zoneinfo.zip</code>
+      has been updated to version 2018i. Note that this ZIP file is
+      only used if a time zone database is not provided by the operating
+      system.
+    </p>
+
+</dl><!-- time -->
+
 <dl id="unsafe"><dt><a href="/pkg/unsafe/">unsafe</a></dt>
   <dd>
     <p><!-- CL 146058 -->