remove 1.8 debugger and added 2.0 debugger

Author: cschiewek

Gemfile

@@ -3,6 +3,6 @@ source "http://rubygems.org"
 gemspec
 
 group :development, :test do
-  gem 'ruby-debug', '>= 0.10.3', :platform => :mri_18
-  gem 'debugger', :platform => :ruby_19
+  gem 'debugger', platform: :ruby_19
+  gem 'byebug', platform: :ruby_20
 end