Verify Moodle 3.5 compliance

[scara]

The code is weekly tested on master and, up to today, it runs fine on master.

Since 3.5 will include even the new Privacy plugins, it will be better to finally test it when RC will be available (e.g. code cleanup) to declare the plugin compliance to 3.5 too.

According to https://docs.moodle.org/dev/Releases#General_release_calendar the 3.5 should be released on 14/05 which gives the opportunity to finally test the compliance to the Privacy API too, due to 24/05.

[scara]

Tested on 161e92e (v1.1.0): https://travis-ci.org/scara/moodle-local_twittercard/builds/379928301.