Testee hangs when running testee with coverage option enabled.

[ivospinheiro]

For instance when we try to execute the tests from the CanJS TodoMVC Guide with the command node_modules/testee/bin/testee index.html --browsers chrome --coverage the testee execution hangs.

After some debugging I discovered that it is required to customize babel plugins/presets in order to run testee with coverage enabled.

Also babel-core and babel-plugin-istanbul should be upgraded to the latest versions.