`catch` is not highlighted in try/catch

[mxthevs]

try is highlighted, catch isn't.

I know catch is not a reserved keyword, but i think it should be highlighted when using it in a try/catch block.

In JavaScript, catch is highlighted.

Can semantic highlighting take care of this?

[cristianoc]

Can be handled the same way async is handled in #603: set to highlighting in the grammar, and semantic highlighting can take care of it when it's used as a variable.