RetractWhileCombing not recognized by version Cura 2.7.0

[lewtwo]

operating system: Linux Mint 18.3 software version: Cura 2.7.0 (PPA)

configure, load new plugin, select "/Downloads/RetractWhileCombing.py" .... Failed to install pluigin from: Invalid Plugin File

Copy file "RetractWhileCombing.py" to plugin directory: /.local/share/cura/2.7/plugins .... no joy

RetractWhileCombing_Documentation.pdf

[lewtwo]

Plugin Version: 15.06.1 URL: https://github.com/Dim3nsioneer/Cura-Plugins/wiki/Retract-While-Combing-plugin

[lewtwo]

Also tested with Cura version 3.2 (Appimage version) with no joy