Check "Scales" options first to continue

[yusufozturk]

Before processing, need to check "Scales" options if it's null or not. Some charts like "Pie chart" etc. may not have "Scales" options.

Error line:
https://github.com/chartjs/chartjs-plugin-annotation/blob/master/src/annotation.js#L36,L37

[lefterisnik]

A quick workaround about this until PR to be merged is:

scales:{
  yAxes: [],
  xAxes: []
},