Use source-map 0.1.34 explicitly.

Hello ben-ng,
I came across this error while using minifyify on some angular and angular-ui scripts:

`` Fatal Error: "" is not in the set ``

The error seems to originate from here:
https://github.com/mozilla/source-map/blob/master/lib/source-map/array-set.js#L71

After some searching around I found this:
https://github.com/mozilla/source-map/pull/121

Which is still unresolved. So maybe minifyify should stay at source-map 0.1.34 until this is resolved?