Update omniauth to version 1.1

I got an error when using omniauth providers on the master branch:

NoMethodError (undefined method `include?' for nil:NilClass):
      oa-core (0.3.2) lib/omniauth/builder.rb:29:in `call' 

This pull request fixes this, I tested with facebook login at least.

Note that one needs to add the corresponding provider gems (like for example omniauth-facebook ), I did not add these to the gemspec.