Remove ruby2.0 exceptions from gemfiles

..since I stopped testing it in rack#184

Author: ktheory

gemfiles/activesupport4.1.gemfile

@@ -4,7 +4,7 @@ source "https://rubygems.org"
 
 gem "activesupport", "~> 4.1.0"
 gem "actionpack", "~> 4.1.0"
-gem "listen", "<= 3.0.6", platforms: [:ruby_20, :ruby_21, :jruby]
+gem "listen", "<= 3.0.6", platforms: [:ruby_21, :jruby]
 
 group :development do
   gem "pry"

gemfiles/activesupport4.2.gemfile

@@ -4,7 +4,7 @@ source "https://rubygems.org"
 
 gem "activesupport", "~> 4.2.0"
 gem "actionpack", "~> 4.2.0"
-gem "listen", "<= 3.0.6", platforms: [:ruby_20, :ruby_21, :jruby]
+gem "listen", "<= 3.0.6", platforms: [:ruby_21, :jruby]
 
 group :development do
   gem "pry"

gemfiles/dalli2.gemfile

@@ -3,9 +3,9 @@
 source "https://rubygems.org"
 
 gem "dalli", "~> 2.0"
-gem "rack", "<= 1.4.7", platforms: [:ruby_20, :ruby_21, :jruby]
-gem "activesupport", "<= 3.2.22.2", platforms: [:ruby_20, :ruby_21, :jruby]
-gem "listen", "<= 3.0.6", platforms: [:ruby_20, :ruby_21, :jruby]
+gem "rack", "<= 1.4.7", platforms: [:ruby_21, :jruby]
+gem "activesupport", "<= 3.2.22.2", platforms: [:ruby_21, :jruby]
+gem "listen", "<= 3.0.6", platforms: [:ruby_21, :jruby]
 
 group :development do
   gem "pry"