I made a small mistake packaging some of the plug-ins, which means that they would not install on Moodle 2.4. Therefore, there are now 3.1.1 versions of the three question bahaviour plugins. Sorry about that.
If you just install the latest version from git, or from the plugins database, you will now get the right code. I just wanted to make sure you did not worry about some, but not all, of the plugins being version 3.1.1, rather than 3.1.
Thanks to Ludovico Romano for spotting the problem and reporting it.