Merge pull request #43 from schwing/prettyprint

PrettyPrint class is included using lowercase 'pp'

lib/github_changelog_generator/parser.rb

@@ -1,6 +1,6 @@
 #!/usr/bin/env ruby
 require 'optparse'
-require 'PP'
+require 'pp'
 require_relative 'version'
 
 module GitHubChangelogGenerator