finish up adding OpenStreetMap as an option. Closes #600.

README.markdown

@@ -257,6 +257,9 @@ Due to recent changes to the Google Maps API, you need a [API Key](https://devel
 	* `HYBRID`
 	* `SATELLITE`
 
+* OpenStreetMap
+	- `osm`
+
 ###Font Options 
 `font:`
 * `AbrilFatface-Average` *Abril Fatface & Average*

website/templates/_make.html

@@ -138,7 +138,7 @@
                 <option value="toner-labels">Stamen Maps: Toner Labels</option>
                 <option value="watercolor">Stamen Maps: Watercolor</option>
                 <option value="sterrain">Stamen Maps: Terrain</option>
-                <option value="osm">Open Street Maps</option>
+                <option value="osm">OpenStreetMap</option>
                 <option value="TERRAIN">Google Maps: Terrain</option>
                 <option value="ROADMAP">Google Maps: Roadmap</option>
                 <option value="HYBRID">Google Maps: Hybrid</option>