Yammer::ApiResponse does not report all successes as successful

[chrisbloom7]

Yammer::ApiResponse#success? is not consistent when reporting on the success of the request. Consider the following:

client = Yammer::Client.new(access_token: access_token) # => #<Yammer::Client:0x007f968faecd10 ...>
current_user = client.current_user # => #<Yammer::ApiResponse:0x007f968fc371e8 @body="...", @code=200, ...>
current_user.class # => Yammer::ApiResponse
current_user.code # => 200
current_user.success? # => true
activity_response = client.create_activity(activity) # => #<Yammer::ApiResponse:0x007f968ff41460 @body="...", @code=202, ...>
activity_response.class # => Yammer::ApiResponse
activity_response.code # => 202
activity_response.success? # => false

I would expect that any response in the 2xx range would report success? as true