Fix errors on Redmine 4.x

[horori]

Thanks for making the wonderful plugin to extend the Redmine API.
After fixing a few lines it works with Redmine 4.1.

Fixed errors:

• An error occurred while loading the routes definition of
  redmine_json_rpc plugin
  (/usr/src/redmine/plugins/redmine_json_rpc/config/routes.rb):
  uninitialized constant ActionController::Routing.
• undefined method `before_filter' for JsonRpcCallController:Class
  (NoMethodError)

Here is my test result to list all the roles

REDMINE=localhost:8080
ADMIN_API_KEY=<APIKEY>
curl -v http://$REDMINE/json_rpc_call.json?key=$ADMIN_API_KEY -X POST -H "Content-Type: application/json" -d '{"class": "Role", "method" : "all", "params" : []}' | jq