Fix errors with the Authorization Grants for OAuth 2.0

[nohorbee]

The list should be clear regarding the Authorization Grant names:

• Authorization code grant: authorization_code
• Resource owner password credentials grant: password
• Client credentials grant: client_credentials
• Implicit grant: implicit
• Refresh token grant: refresh_token

#%RAML 0.8
title: My Sample API
securitySchemes:
    - oauth_2_0:
        description: |
            OAuth 2.0 implementation.
        type: OAuth 2.0
        settings:
          authorizationUri: https://www.myapi.com/1/oauth2/authorize
          accessTokenUri: https://www.myapi.com/1/oauth2/token
          authorizationGrants: [ authorization_code, password, client_credentials, implicit, refresh_token ]

[aldonline]

Let's take the opportunity to fix it and make it right ( see: #177 )

[usarid]

In fact refresh_token is not a grant type. Confusingly, in OAuth 2.0, to use a refresh token (which MAY be obtained with one of the grant type that issues refresh tokens) to obtain another access token, you submit a request with a parameter called grant_type whose value is set to refresh_token. But there is no notion of an API that supports this grant type as it's not a type of authorization grant. Let's remove it from the list.

[sichvoge]

In summary, RAML 1.0 will have the following OOTB grant types

• Authorization code grant: authorization_code
• Resource owner password credentials grant: password
• Client credentials grant: client_credentials
• Implicit grant: implicit