fix minitest problem

**This is a potential breaking change for some users.**

I have updated the changelog with details and links to the minitest homepage.

Fixes the problem by _not_ including `Test::Unit::Assertions` in the Operations module.

I tried several other fixes, but could not find any that were compatible across ruby 1.9.3 and ruby 2.*

### Tests

* tests that `calabash-ios version` reports version without error
* tests that `calabash-ios console` exits cleanly

```
$ script/ci/travis/local-run-as-travis.rb
```