Fix specs

Hi, I forked this repo and ran the specs, but then I received the following errors:

<pre>
Failures:

  1) Authy::Response should be ok if the return code is 200
     Failure/Error: @response.ok?.should be_true
       expected true to respond to `true?`
     # ./spec/authy/response_spec.rb:17:in `block (2 levels) in <top (required)>'

  2) Authy::API verificating tokens should fail to validate a given token if the user is not registered
     Failure/Error: response.ok?.should be_false
       expected false to respond to `false?`
     # ./spec/authy/api_spec.rb:53:in `block (3 levels) in <top (required)>'
</pre>

This PR fix this problem.