Include tests for the `enable` feature 

Fixed it to run in non-browser environment


@jtangelder, the second [commit](https://github.com/ppcano/hammer.js/commit/d346fba59ccf78cd7616a7d32568e7d17939c56c) changes some validation with recognizer.enable property. 

When this parameter is a function, the `input` and `recognizer` parameter should be passed.