[gfm] Remove incorrect information

Fenced code blocks *do* have syntax highlighting.

Author: 0b10011

mode/gfm/index.html

@@ -33,7 +33,7 @@ <h1>CodeMirror: GFM mode</h1>
 
 Underscores_are_allowed_between_words.
 
-## Fenced code blocks (and syntax highlighting... someday)
+## Fenced code blocks (and syntax highlighting)
 
 ```javascript
 for (var i = 0; i &lt; items.length; i++) {