Updated Dependencies

After updating the deps to latest versions I got following problem:
```bash
λ bennyklotz spinach-sinatra-demo → λ git master* → rake                                 

Feature: Application test

  Scenario: Hello world
    ✔  Given I am on the front page        # features/steps/test.rb:3
    !  Then I should see a salutation      # features/steps/test.rb:7

        undefined method `must_equal' for true:TrueClass
        /home/benny/Web/ruby/spinach-sinatra-demo/features/steps/test.rb:8:in `block in <class:ApplicationTest>'

  Scenario: Goodbye
    ✔  Given I am on the front page        # features/steps/test.rb:3
    ✔  When I click on the first link      # features/steps/test.rb:11
    !  Then I should see goodbye           # features/steps/test.rb:15

        undefined method `must_equal' for true:TrueClass
        /home/benny/Web/ruby/spinach-sinatra-demo/features/steps/test.rb:16:in `block in <class:ApplicationTest>'

Error summary:
  Errors (2)
    Application test :: Hello world :: Then I should see a salutation
    Application test :: Goodbye :: Then I should see goodbye


Steps Summary: (3) Successful, (0) Pending, (0) Undefined, (0) Failed, (2) Error

Finished in 0.033637557 seconds
```
Therefore I had to require minitest/autorun in https://github.com/Benny1992/spinach-sinatra-demo/blob/master/features/support/env.rb#L4