cordova plugin add https://github.com/devgeeks/VolumeSlider.git fails

[schumannd]

I am using npm version 5.0.3 and cordova version 7.0.1 This is the error I get when executing cordova plugin add https://github.com/devgeeks/VolumeSlider.git:

Error: Failed to fetch plugin https://github.com/devgeeks/VolumeSlider.git via registry.
Probably this is either a connection problem, or plugin spec is incorrect.
Check your connection and plugin name/version/URL.
Error: npm: Command failed with exit code 1 Error output:
npm ERR! cb() never called!

npm ERR! This is an error with npm itself. Please report this error at:
npm ERR!     <https://github.com/npm/npm/issues>

Other plugins install just fine