providers/plainbox-provider-checkbox: increment version to 0.16.1
"automatic merge of lp:+branch/checkbox/release/ by tarmac [r=sylvain-pineau][bug=1331302,1341769,1347120,1382321,1383447,1387782,1387843,1388055,1388747,1389253,1399481][author=checkbox-dev]"