doc/go1.3.html: minor tweak of Solaris wording

Discussion here: https://golang.org/cl/100490044/#msg14

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/98350043

doc/go1.3.html

@@ -89,7 +89,7 @@ Go 1.3 now includes experimental support for Plan 9 on the <code>386</code> (32-
 <h3 id="solaris">Support for Solaris</h3>
 
 <p>
-Go 1.3 now includes experimental support for Solaris on the <code>amd64</code> (64-bit x86) architecture. It uses illumos, equivalent to Solaris 11 or above.
+Go 1.3 now includes experimental support for Solaris on the <code>amd64</code> (64-bit x86) architecture. It requires illumos, Solaris 11 or above.
 </p>
 
 <h2 id="memory">Changes to the memory model</h2>