Apply Style/ColonMethodCall rubocop rule

This rule seems to be an obvious one, but we weren't following it in one
place.

config/initializers/graphql_api.rb

@@ -4,7 +4,7 @@ module GraphQLApi
       if ActiveRecord::Base.connection.tables.any?
         api_config = YAML.load_file("./config/api.yml")
         GraphqlController.const_set "API_TYPE_DEFINITIONS",
-          GraphQL::ApiTypesCreator::parse_api_config_file(api_config)
+          GraphQL::ApiTypesCreator.parse_api_config_file(api_config)
       end
     end
   end