"is" keyword is not highlighted

[sumanthratna]

GitHub's markdown correctly highlights is, but it's not highlighted in Atom.
For example:

try {
    await API.makeCall();
} catch(e) {
    if (e is SocketException) {
        /*do something*/
    }
}

I took a look at grammars/dart.cson and it appears that the is keyword has been accounted for. I'm not great with RegExes so I can't directly fix it, but I think it's where the problem lies.