Joplin is built from pre-release instead of stable versions

Joplin, as available on F-Droid, uses pre-release versions instead of stable versions. For example, the current version available at https://f-droid.org/packages/net.cozic.joplin is 3.1.2 which, as of right now, is a pre-release (see https://github.com/laurent22/joplin-android/releases/tag/android-v3.1.2). The current stable version of Joplin for Android is 3.0.7 (see https://github.com/laurent22/joplin-android/releases).

While Joplin's pre-release versions are usually stable enough, there still contain some breaking bugs, which are not acceptable when the user expects to have a 100% stable experience. Another problem is that F-Droid doesn't mark those versions as pre-release, so the user will think that they are stable versions.