Add default (missing) :client_options

This fixes `NoMethodError - undefined method 'ca_path' for nil:NilClass:` error when no :ssl options are defined.

More details about the error:
> NoMethodError - undefined method `ca_path' for nil:NilClass:
>   omniauth-deezer (0.2.0) lib/omniauth/strategies/deezer.rb:46:in `callback_phase'
>   omniauth (1.0.3) lib/omniauth/strategy.rb:204:in `callback_call'
>   omniauth (1.0.3) lib/omniauth/strategy.rb:166:in `call!'