Fix spaces in rectangle_zone usage comment

Author: Jesse Emond

lib/open_weather/api.rb

@@ -29,7 +29,7 @@ def cities(ids, options = {})
     end
 
     # Bounding box (lat and lon of top left and bottom right points, map zoom)
-    # Usage: OpenWeather::Current.rectangle_zone(12,32,15,37,10)
+    # Usage: OpenWeather::Current.rectangle_zone(12, 32, 15, 37, 10)
     def rectangle_zone(top_left_lat, top_left_lon,
                        bottom_right_lat, bottom_right_lon,
                        map_zoom, options = {})