Missing credentials param in password_access_token_request.rb

[grun00]

Hey, I noticed that the initializer method in password_access_token_request.rb is missing the credentials param and when I try to request a token I get the following error:

ArgumentError (wrong number of arguments (given 5, expected 3..4)):

Adding the param in the gem seems to fix the issue.

it is like this:

        def initialize(server, client, resource_owner, parameters = {})

it should be like:

        def initialize(server, client, credentials, resource_owner, parameters = {})

Is someone planning on fixing this? I could add a PR.

The commit that created the problem in the doorkeeper gem

[grun00]

Someone already opened a PR about it (#153)