Fix #33 rubocop conflict

- rubocop v0.16.0 does not work with newly-released rainbow 2.0.0
- rubocop v0.17.0 does not work with chef 11.8.2 due to json dependency
  hell
- we either need to explicitly include rainbow 1.99.2 in this cookbook
  (bad idea), or we need to update to bleeding edge version of chef
- bleeding edge version of chef fixes json dependency problem, but
  breaks chefspec, so we need bleeding edge version of chefspec as well
Merge pull request #34 from jhx/issue_33_fix_rubocop_conflict

Fix #33 rubocop conflict