"3.1.0dev" (which isn't the an actual release / done yet) was accidentally "released" via Ubuntu PPA for a couple of older Ubuntu releases
I recommend downgrading to 3.0.x via the stable series, not sure if I'm going to add a fake 3.1.0dev2 (which is 3.0.x) to PPA in order to fix this, perhaps better to just focus on getting the real 3.1.0dev (and call it 3.1.1dev) out...