README - yml syntax fixed

Author: priyashantha

README.md

@@ -16,7 +16,7 @@ You can also search for locations using the search box, which uses the Google Ma
 |`field_names`|See `GoogleMapField.yml`'s `default_options.field_names`|A map of field names to save the map data into your object.|
 
 ##### make sure `api_key` config added in site yml file
-```$xslt
+```yml
 BetterBrief\GoogleMapField\GoogleMapField:
   default_options:
     api_key: 'GOOGLE_API_KEY'