Allow use of custom obfuscator version

[derrickb]

As seen in this fork:
arekzelechowski@0f1d1b1

This is really useful as it allows for decoupling of the plugin from the obfuscator version, and also allows us to specify a version of the obfuscator which is sometimes required (eg. if a bug was present in latest).

[raphinesse]

Instead of adding an option, this package could also change javascript-obfuscator to a peer dependency.

[derrickb]

Instead of adding an option, this package could also change javascript-obfuscator to a peer dependency.

Even better!