Fix: use compatible ActiveSupport and Middleman
Fix: use compatible ActiveSupport and Middleman

Otherwise, the following happens on Travis:

Bundler could not find compatible versions for gem "activesupport":
  In Gemfile:
    actionpack (~> 4.0) was resolved to 4.2.5, which depends on
      activesupport (= 4.2.5)

    middleman-core (~> 3.3.0) was resolved to 3.3.8, which depends on
      activesupport (~> 4.1.0)

Fullscreen/bh,Fullscreen/bh