Fix rubocop offense

Author: ceritium

actioncable/lib/rails/generators/channel/channel_generator.rb

@@ -67,7 +67,7 @@ def import_channels_in_javascript_entrypoint
 
         def import_channel_in_javascript_entrypoint
           append_to_file "app/javascript/channels/index.js",
-            using_node? ? %(import "./#{file_name}_channel"\n) : %(import "channels/#{file_name}_channel"\n)       
+            using_node? ? %(import "./#{file_name}_channel"\n) : %(import "channels/#{file_name}_channel"\n)
         end
 
         def install_javascript_dependencies