upgrade to gerrit 3.2

gerrit 3.2 is going to be released in about two weeks from now.

the major user-visible improvements since the 3.0 release relate to performance, both in the gui and when interacting with git. on the admin side, metrics and logging have been added/improved. i'm not aware of major user-visible features i could pitch here, only a lot of polishing of the new polygerrit UI. a lot changed behind the scenes (esp. on the UI side), so this should be taken as an intermediate step to make the upgrade to the next major feature release (3.3 according to plan) less painful.

https://www.gerritcodereview.com/3.1.html
https://www.gerritcodereview.com/3.2.html