Registering the Plugin

[fireflysemantics]

Just a little note about the registration part of the readme.

I think it should be.

Registering
All charts

Chart.register(gradient);
Single chart

const chart = new Chart(ctx, {
  // ...
  plugins: [gradient]
});

So per this SO question plugins should be an array, and I also changed Signle to Single ...

Thanks for making this plugin. It rocks!!