Ruby 2.7 keyword parameter deprecation warning in OAuth2::Client#get_token

Created by: stanhu

Running bundle exec exec rspec -w, I see this deprecation warning:

OAuth2::Strategy::Password
  #get_token (json)
/Users/stanhu/github/oauth2/lib/oauth2/strategy/password.rb:25: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/Users/stanhu/github/oauth2/lib/oauth2/client.rb:161: warning: The called method `get_token' is defined here

I sort of regret mixing positional and keyword arguments now.