doc/go1.7.html: make RFC an actual link

Change-Id: I5e8dad0c2534b5c3654cf0a0b51a38186d627a3c
Reviewed-on: https://go-review.googlesource.com/23582Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.7.html

@@ -535,7 +535,8 @@ generated by the new <code>BestSpeed</code>.
 
 <p>
 It is important to note that both
-<code>BestSpeed</code> and <code>HuffmanOnly</code> produce a compressed output that is RFC 1951 compliant.
+<code>BestSpeed</code> and <code>HuffmanOnly</code> produce a compressed output that is
+<a href="https://tools.ietf.org/html/rfc1951">RFC 1951</a> compliant.
 In other words, any valid DEFLATE decompressor will continue to be able to decompress these outputs.
 </p>