update bundle version

Author: Ruslan Korolev

haml-rails.gemspec

@@ -22,7 +22,7 @@ Gem::Specification.new do |s|
   s.add_dependency "html2haml",     [">= 1.0.1"]
 
   s.add_development_dependency "rails",   [">= 4.0.1"]
-  s.add_development_dependency "bundler", "~> 1.2"
+  s.add_development_dependency "bundler", "~> 1.7"
   s.add_development_dependency "rake"
   s.add_development_dependency 'appraisal', '~> 1.0'