drop 1.8 support and add 2.0

As MRI 1.8 is EOL, I think it is okay to drop 1.8 support.

.travis.yml

@@ -1,15 +1,10 @@
 bundler_args: --without development
 language: ruby
 rvm:
+  - 2.0.0
+  - jruby-20mode
+  - rbx-20mode
   - 1.9.3
-  - jruby-18mode
   - jruby-19mode
-  - rbx-18mode
   - rbx-19mode
-  - 1.8.7
 script: thor spec
-matrix:
-  allow_failures:
-    - rvm: 1.8.7
-    - rvm: rbx-18mode
-    - rvm: jruby-18mode

lib/zero.rb

@@ -1,8 +1,3 @@
-# Only add fixes, if needed to avoid an unnecessary installed gem
-if RUBY_VERSION <= '1.9'
-  require 'zero_fix18'
-end
-
 module Zero
   require 'zero/controller'
   require 'zero/router'

zero.gemspec

@@ -20,5 +20,4 @@ Gem::Specification.new do |s|
   s.rubygems_version = '1.8.24'
 
   s.add_dependency('tilt')
-  s.add_dependency('zero-fix18') if RUBY_VERSION <= '1.9' 
 end