Is there a reason you have an "optimistic" version constraint (>=) for the uglifier gem? Bascially, you are saying that all versions of this gem greater than or equal to 1.3.0 will work. A "pessimistic" version constraint (~>) will keep the gem at a patch level. For instance: 

gem 'sass-rails', '~> 4.0.0' will install version 4.0.0, 4.0.1, 4.0.2 and so on. It will not install minor versions like 4.1.0, 4.2.0, 4.3.0, and so on unless you specify gem 'sass-rails', '~> 4.0'.