doc/go1.12: release notes for lib/time

Change-Id: Ic435090bda64d1061f2c3aac0aa94ed7a4800b0b
Reviewed-on: https://go-review.googlesource.com/c/152743Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.12.html

@@ -381,7 +381,7 @@ for {
 <dl id="lib/time"><dt><a href="/pkg/lib/time/">lib/time</a></dt>
   <dd>
     <p><!-- CL 151299 -->
-      TODO: <a href="https://golang.org/cl/151299">https://golang.org/cl/151299</a>: update tzdata to 2018g
+    The time zone database in <code>$GOROOT/lib/time/zoneinfo.zip</code> has been updated to version 2018g. Note that this ZIP file is only used if a time zone database is not provided by the operating system.
     </p>
 
 </dl><!-- lib/time -->