You have omitted some code and added in other unneeded code.
Try:
` # Load the normal support files.
require 'sketchup.rb'
require 'extensions.rb'
ext = SketchupExtension.new('pluginName', File.join('pluginFolder', 'pluginLoader.rb'))
# Optionally 'name' the Extension - it can differ from the registered name.
ext.name = 'pluginName'
ext.creator = 'xxxxx'
ext.version = '1.0.0'
ext.copyright = '2016, xxxxxxxx'
ext.description = 'xxxxxxxxxxxxxxxxxxx'
# This 'path' is NOT needed.
ext.extension_path=File.join(File.dirname(FILE), "pluginFolder" )
Sketchup.register_extension(ext, true)`
Add in the bold code and remove the struck-through code...