Limit version of sprokets to less than four

Later versions of sprokets which are included with rails require setting
up a manifest file for assets

See: rails/sprockets-rails#444

wakes.gemspec

@@ -29,8 +29,10 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'google-api-client'
   spec.add_dependency 'httparty', '~> 0.13'
   spec.add_dependency 'rails', '>= 4.2.4'
+  spec.add_dependency 'sprockets', '<4'
   spec.add_dependency 'redis'
   spec.add_dependency 'redis-namespace'
+  spec.add_dependency 'sprockets', '<4'
 
   spec.add_development_dependency 'bundler'
   spec.add_development_dependency 'combustion'