Update Minetest to latest stable version

I got tired of waiting for someone else to update this app, so I decided to jump I myself and do the updating.

I tried to use fdroid build on this app, but it failed, probably because my Android SDK and/or NDK haven't been set up yet for my fdroiddata copy, although I'm sure that they will build successfully on the official fdroidserver.

#784 Metadata for Minetest is not set to check for any updates whatsoever.