grunt.registerTask(taskName, fn) fails

Apologies if I'm doing this wrong.

In Grunt 0.4, according to http://gruntjs.com/creating-tasks#basic-tasks, the method signature for grunt.registerTask is:

    grunt.registerTask(taskName, [description, ] taskFunction)

Where taskFunction can be a string, an Array, or a function. However, when grunt-retro is in use, calling registerTask with the signature

    grunt.registerTask(taskName, function() { ... })

fails with "TypeError: Object function foo() { ... has no method 'split'"

The attached pull request fixes the issue and the tests still pass.