doc/go1.3.html: go test always builds

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/89370043

doc/go1.3.html

@@ -152,6 +152,12 @@ when the race detector is enabled, to eliminate false reports about unsafe
 access to coverage counters.
 </p>
 
+<p>
+The <a href="/cmd/go/"><code>go test</code></a> subcommand
+now always builds the package, even if it has no test files.
+Previously, it would do nothing if no test files were present.
+</p>
+
 <p>
 Finally, the go command now supports packages that import Objective-C
 files (suffixed <code>.m</code>) through cgo.