[Eng] use nile release instead of building from source

[ohadschn]

I talked to the maintainer, and hopefully he'll issue a new release soon (imLinguin/nile#63). Once that happens we should:

• Update docs
• Update Dockerfile

BTW In the future this might be a non-issue: imLinguin/nile#64 (if I get the time I might implement it myself)