Broken SampleApp demo

[tonxxd]

In the sampleApp demo
https://pgmlearning.herokuapp.com/samplingApp
mentioned in the sampling method chapter scripts are not loaded when visiting the demo through https due to mixing http and https connections.

In particular
http://d3js.org/d3.v4.min.js
and
http://dimplejs.org/dist/dimple.v2.3.0.min.js
which prevent the demo from computing samples

Just changing urls to the https versions should fix the issue