Correct JXA language grammar definition
Correct JXA language grammar definition

Modify to work with newer [language-javascript-jxa](https://atom.io/packages/language-javascript-jxa) package.

Signed-off-by: Daniel Bayley <a8999ec6105921a5e047cd21489d1a78436cfb40@me.com>

rgbkrk/atom-script,fscherwi/atom-script,idleberg/atom-script