Bug#1017609: ruby-terser: Test fails with node-terser >= 5

[Yadd]

ruby-terser uses a patched terser.js (see 
https://github.com/ahorek/terser-ruby/blob/master/patches/terser-sync.patch)

So this issue is simple to fix: copy node-terser files into 
vendor/terser and patch it using upstream patch.

Cheers,
Yadd