Match a smaller pattern for JS Argument Lists

Matching the entire invocation just to pull out the JavaScript argument
list was dumb. There's too many variations of how an invocation can be
written for that to be reliable.

Instead, just match a list of things after a colon. This narrows the
search and allows for thing such as the subject of an invocation being
an invocation in and of itself.

Take the following code for example. It used jQuery to find the source
element of an HTML audio player and change its `src` to a song's URL.

  ((player find:"source") attr:"src", (song url))

It's much easier (and reliable) to only worry about the part after
"attr:" and not compensate for all the ways you can write the beginning
of the invocation.