Remove "node-zopfli" dependency which is not maintained anymore

[boehmers]

Hi,

while trying to run npm install in your project i got an error while trying to download a pre-compiled node-zopfli. Therefore, the build-process falls back to building the package with g++ on my machine, which also fails because of missing g++. This is not my problem here because simply installing g++ helped, but after researching the problem i found this issue in the node-zopfli project:
pierreinglebert/node-zopfli#87

This issue was opened on 23 May 2017 and is also the most commented issue of the project. 4 days ago, it was reported that the project is no longer maintained (see linked issue above).

IMHO no longer maintained dependencies should be removed or replaced.

Thanks in advance!

[boehmers]

Okay nevermind, just saw you are working on much more than only removing this one dependency :-)