New: Support TypeScript 2.5 (fixes #368)

[azz]

Only change made was to support optional catch binding:

try {} catch {}
try {} catch {} finally {}

I've done so in the same way that babylon has done, setting param to null on the CatchClause.

Might want to hold out and wait for the full release?

[eslintbot]

LGTM

[JamesHenry]

Thanks! I have changed the base to be a new ts-2.5 branch. We will do what we did last time, keep 2.5 on a protected parallel branch to master until it becomes the stable release