Change syntax highlighting to JSON

The code is JSON but, more importantly, this should act as an indirect fix to #25 and any similar issues in the future.

Author: Hoolean

index.md

@@ -7,7 +7,7 @@ title: GeoJSON
 
 GeoJSON is a format for encoding a variety of geographic data structures.
 
-{% highlight javascript %}
+{% highlight json %}
 {
   "type": "Feature",
   "geometry": {