fix: OAuth20Service::refreshAccessToken should use RefreshTokenEndpoint, not AccessTokenEndpoint (thanks to https://github.com/vivin)
fix: OAuth20Service::refreshAccessToken should use RefreshTokenEndpoint, not AccessTokenEndpoint (thanks to https://github.com/vivin)

scribejava/scribejava,XeroAPI/scribe-java,fernandezpablo85/scribe-java