remove options.modules in babelTranspile

[wyntau]

options.modules = 'system' is deprecated in Babel 6

And this will lead to error

Using removed Babel 5 option: base.modules - Use the corresponding module transform plugin in the plugins option. Check out http://babeljs.io/docs/plugins/#modules(…)

[wyntau]

I make a demo to use systemjs and babel to load es6 module directly in browser. The demo will work only when I commen out options.modules = 'system'

[wyntau]

Can anyone review this PR please?

[guybedford]

The options.modules is critical to the Babel 5 support in this project. This feature will be deprecated though, and as such does not support Babel 6.