Apparently Chart.pluginService is deprecated, but this name is still used in the documentation. I suggest to update it :)
### Creating Plugins
-Starting with v2.1.0, you can create plugins for chart.js. To register your plugin, simply call `Chart.pluginService.register` and pass your plugin in.
+Starting with v2.1.0, you can create plugins for chart.js. To register your plugin, simply call `Chart.plugins.register` and pass your plugin in.
Plugins will be called at the following times
* Start of initialization
* End of initialization