Update build for travis environment and gem dependency changes

Author: Jared Deckard

.travis.yml

@@ -5,7 +5,6 @@ install:
   - ./script/bootstrap
 script: ./script/cibuild
 rvm:
-  - 1.9.3
   - 2.0
   - 2.1
   - 2.2

script/bootstrap

@@ -6,4 +6,4 @@ if ! bundle check 1>/dev/null 2>&1; then
 fi
 
 npm install
-bower install --no-color
+./node_modules/bower/bin/bower install --no-color

task_list.gemspec

@@ -16,13 +16,13 @@ Gem::Specification.new do |gem|
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
   gem.require_paths = ["lib"]
 
-  gem.required_ruby_version = ">= 2.1.0"
+  gem.required_ruby_version = ">= 2.0.0"
 
   gem.add_dependency "activesupport", "~> 4.0" if RUBY_VERSION < '2.2.2'
   gem.add_dependency "nokogiri", "~> 1.6.0" if RUBY_VERSION < '2.1.0'
   gem.add_dependency "html-pipeline"
 
-  gem.add_development_dependency "github-markdown"
+  gem.add_development_dependency "commonmarker"
   gem.add_development_dependency "rake"
   gem.add_development_dependency "coffee-script"
   gem.add_development_dependency "json"