doc/go1.7.html: fix name of tls.Config.NextProtos

Updates #16737

Change-Id: Ia51fc9b06df43b7c6f7136e90b40362263c20081
Reviewed-on: https://go-review.googlesource.com/27126Reviewed-by: Chris Broadfoot <cbro@golang.org>

doc/go1.7.html

@@ -909,7 +909,7 @@ For example, the address on which a request received is
 <p>
 The server's <a href="/pkg/net/http/#Server.Serve"><code>Serve</code></a> method
 now only enables HTTP/2 support if the <code>Server.TLSConfig</code> field is <code>nil</code>
-or includes <code>"h2"</code> in its <code>TLSConfig.NextProto</code>.
+or includes <code>"h2"</code> in its <code>TLSConfig.NextProtos</code>.
 </p>
 
 <p>