This addon is not installable as a zip file. You need to copy it under your addons folder manually. The dev did a proper class but did not bother to wrap as a zip file.
run the line in the python console in Blender bpy.utils.script_path_user()
and under there find the addon folder, that is where you put that .py
You can also install my DuWamf addon and access those folders easily. You can just use the free version.