Bump ruby version to 2.1

Author: pmgrove

zendesk_apps_tools.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |s|
   s.summary     = 'Tools to help you develop Zendesk Apps.'
   s.description = s.summary
 
-  s.required_ruby_version = '>= 2.0'
+  s.required_ruby_version = '>= 2.1'
   s.required_rubygems_version = '>= 1.3.6'
 
   s.add_runtime_dependency 'thor',        '~> 0.19.4'