Update required for Gibbon 2.0

[Daniel Kehoe]

Gibbon 2.0.0 was released July 29, 2015.

When you run bundle install or bundle update the newest Gibbon 2.0 gem will be installed and the application will error with

NameError: uninitialized constant Gibbon::API

Either change the Gemfile and specify

gem 'gibbon',  '~>1.2.0'

or update the code that uses Gibbon.

See amro/gibbon#131