Use backticks for WOF source names

search.md

@@ -291,7 +291,7 @@ The search examples so far have returned a mix of results from all the data sour
 |---|---|---|
 | [OpenStreetMap](http://www.openstreetmap.org/) | `openstreetmap` | `osm` |
 | [OpenAddresses](http://openaddresses.io/) | `openaddresses` | `oa` |
-| [Who's on First](https://whosonfirst.mapzen.com) | 'whosonfirst' | 'wof' |
+| [Who's on First](https://whosonfirst.mapzen.com) | `whosonfirst` | `wof` |
 | [GeoNames](http://www.geonames.org/) | `geonames` | `gn` |
 
 If you use the `sources` parameter, you can choose which of these data sources to include in your search. So if you're only interested in finding a YMCA in data from OpenAddresses, for example, you can build a query specifying that data source.