allow newer omniauth-oauth2 versions

[yhontar]

No description provided.

[dalezak]

Any plans / hopes on this getting merged? Running into a version issue.

Bundler could not find compatible versions for gem "omniauth-oauth2":
  In snapshot (Gemfile.lock):
    omniauth-oauth2 (= 1.7.1)

  In Gemfile:
    omniauth-clever was resolved to 1.2.1, which depends on
      omniauth-oauth2 (~> 1.1.1)

Or is there a fork others are using instead of clever/omniauth-clever?

[cycomachead]

This would definitely be a help in some of my projects!