Log Message:
Update ruby-rainbow to 2.2.2.

# 2.2.0 (2016-12-27)

* improved Windows support
* added Ruby 2.4 support
* added `bold` alias method for `bright`

# 2.2.1 (2016-12-28)

* fixed gem installation (2.2.0 was a broken release)

# 2.2.2 (2017-04-21)

* added explicit rake dependency to fix installation issue