Replace deprecated String.prototype.substr()

String.prototype.substr() is deprecated (see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr) so we replace it with slice() which works similarily but isn't deprecated.
Signed-off-by: Tobias Speicher <rootcommander@gmail.com>

app/assets/javascripts/osm.js.erb

@@ -146,7 +146,7 @@ OSM = {
       return args;
     }
 
-    hash = Qs.parse(hash.substr(i + 1));
+    hash = Qs.parse(hash.slice(i + 1));
 
     var map = (hash.map || '').split('/'),
       zoom = parseInt(map[0], 10),