doc/go1.12: fix minor grammatical error

Change-Id: I767bf77aeab62f2d42239fac9d601a8e04fe860f
Reviewed-on: https://go-review.googlesource.com/c/154957Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.12.html

@@ -279,7 +279,7 @@ for {
 <p><!-- CL 141977 -->
   <code>go</code> <code>doc</code> now supports the <code>-all</code> flag,
   which will cause it to print all exported APIs and their documentation,
-  similarly to what the <code>godoc</code> command line used to do.
+  as the <code>godoc</code> command line used to do.
 </p>
 
 <h3 id="trace">Trace</h3>