Use a trick to make RubyGems allow pre releases

Author: rafaelfranca

sass-rails.gemspec

@@ -16,7 +16,7 @@ Gem::Specification.new do |s|
   s.add_dependency 'railties',        '>= 4.0.0', '< 5.0'
   s.add_dependency 'sass',            '~> 3.4'
   s.add_dependency 'sprockets-rails', '< 4.0'
-  s.add_dependency 'sprockets',       '>= 4.0.0.beta1'
+  s.add_dependency 'sprockets',       '~> 4.x'
 
   s.add_development_dependency 'sqlite3'