Set a sort order for the samples.json file's content

This PR sets the sort order of the `samples.json` file's content once and for all.
The order of results from [Dir.entries()](http://ruby-doc.org/core-2.1.2/Dir.html#glob-method) depends on the system. This results in the `samples.json` file being considered as completely changed by git.

Thus, this PR should reduce the number of changes made to `samples.json` in future PR and the number of conflicts on this file.