games/anki: Update to 2.1.15

Changelog:

• The V2 scheduler now fully randomizes review cards due on a given day.
• Fix flag changes in Browse screen not syncing.
• Cleanup recording wav file when recording canceled.
• Fix the window icon on Wayland.
• Add a progress bar to media deletion.
• Other minor changes.

https://apps.ankiweb.net/docs/changes.html#changes-in-2.1.15

MFH: 2019Q3