Switch test framework to midje

Midje can be used in the further development to mock function calls
which can not be done with clojure.test.

Resolves issue-8
Switch TravisCI to midje
Fix lein plugin dependency
Merge pull request #14 from bertschneider/issue-8

Switch test framework to midje

Midje can be used in the further development to mock function calls
which can not be done with clojure.test.

Resolves issue-8