asset-check: Minor code clean up

* Whitelist non-standard global 'phantomjs' to satisfy jshint.
* Move regex execution in parseArgument() to after the early
  return where it wasn't being used.
* Whitespace in object literlas and function call line continuation.
* Fix masked error where regex result array was casted to a string
  inside bracket access.
* Most inline commments didn't end in a full stop, make them
  consistent by removing it from the two comments that did.

Change-Id: Ica8dbc689cf5c6da4c18a29daeb386d638fccc0b