language: ruby
rvm:
  - 2.1.5
  - 2.2.2

language: ruby
rvm:
  - 2.1.5
  - 2.2.2
before_install:
  - gem install bundler

Fix Travis CI issue "undefined method `spec` for nil:NilClass"
Fix Travis CI issue "undefined method `spec` for nil:NilClass"

A newish verison of rubygems (v2.6.13) and an oldish version of bundler (v1.7.6) don't play well together, resulting in the above error when bundling.

Updating the version of bundler Travis CI provides to a newer version fixes this problem.
