doc: change go1.6 http heading

Change-Id: Iae05082530891175e9c86da244e610bc92759561
Reviewed-on: https://go-review.googlesource.com/17918Reviewed-by: Chris Broadfoot <cbro@golang.org>

doc/go1.6.html

@@ -33,7 +33,7 @@ We expect almost all Go programs to continue to compile and run as before.
 <p>
 The release adds new ports to <a href="#ports">Linux on 64-bit MIPS and Android on 32-bit x86</a>;
 defined and enforced <a href="#cgo">rules for sharing Go pointers with C</a>;
-transparent, automatic <a href="#http">support for HTTP/2</a>;
+transparent, automatic <a href="#http2">support for HTTP/2</a>;
 and a new mechanism for <a href="#template">template reuse</a>.
 </p>
 
@@ -258,7 +258,7 @@ to implementations of the
 
 <h2 id="library">Core library</h2>
 
-<h3 id="http">HTTP</h3>
+<h3 id="http2">HTTP/2</h3>
 
 <p>
 Go 1.6 adds transparent support in the