Remove colorize dependency

We've had a few complaints about `haml-lint` pinning the version of
`colorize` to an old version (understandably so). This was done to fix a
change in behavior where `colorize` would still output color escape
sequences even when the output was redirected to a non-TTY.

At the cost of implementing colors ourself, this is now handled entirely
by the `Logger` class, so the dependency on `colorize` can be removed.

Change-Id: Iab226c4900266fdc12de4266eadfa9568cedee2c
Reviewed-on: http://gerrit.causes.com/40430
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

haml-lint.gemspec

@@ -21,7 +21,6 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '>= 1.9.3'
 
-  s.add_dependency 'colorize', '0.5.8'
   s.add_dependency 'haml', '>= 4.0'
   s.add_dependency 'rubocop', '>= 0.24.1'
   s.add_dependency 'sysexits', '~> 1.1'

lib/haml_lint/reporter/default_reporter.rb

@@ -1,5 +1,3 @@
-require 'colorize'
-
 module HamlLint
   # Outputs lints in a simple format with the filename, line number, and lint
   # message.