Problems with CLI options getting merged instead of overwritten

[pahen]

By looking at the code it seems this behavior is intended, but it seems kind of strange to merge instead of overwrite the options in some cases. Consider the following example:

Running with browsers = ['Chrome', 'PhantomJS']; in testacular.conf.js:

$ testacular start --browsers=PhantomJS

Will run the tests in both Chrome and PhantomJS, which I think is kind of unexpected behavior.