Strip comments in JSON by parsing instead of regex

As requested in https://github.com/jshint/jshint/pull/1567

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Using regex for this is just too fragile.

I've changed it out to use the strip-json-comments module instead: https://github.com/sindresorhus/strip-json-comments

Example of where the existing one will fail:

    console.log(removeComments('{"a":"b//c"}'));
    //=> {"a":"b