Clean up the gemspec
Just add files know to git to the gem

This is the vanilla bundler approach
Remove hashie dependency
Only use client_supplied_id if provided by user
Move dependencies from Gemfile to gemspec
Relax faraday dependency to 0.7.6
Update specs to new rspec syntax
Require lowest supported rspec version
Require rake 10.x for development

This is the vanilla bundler approach
Add bundler as a development dependency