Add `mocha` option to allow overriding Mocha

This feature allows users to supply the plugin with a version of Mocha
of their choosing. This means the latest version of Mocha can be
injected without needing to update this task, and older versions of
Mocha can be used in test environments that depend on deprecated
behavior.
Invalid require cache to allow multiple test runs in the same process

This fix a behaviour causing grunt-watch with "spawn: false" option to play badly with grunt-mocha-test. This fix should hopefully make things better.
Updating travis-cov to work with latest NPM
Merge branch 'specify-mocha' of https://github.com/jugglinmike/grunt-mocha-test into jugglinmike-specify-mocha
Added an extra test to verify that the clearRequireCache option does not break the require option
updating dependencies
version 0.8.0
added vagrant halt shortcut
Edit lib/MochaWrapper to force delete require.cache