Finish upgrading Gradle wrapper from 2.0 => 2.1
Finish upgrading Gradle wrapper from 2.0 => 2.1

Commit 4d4787d updated the Gradle wrapper config from 2.0 => 2.1, but
did not actually update the wrapper properties file (forgot to run
`gradle wrapper`). This commit finishes what was started there.

bisq-network/exchange,myteer/bitsquare,myteer/bitsquare,haiqu/bitsquare,ManfredKarrer/exchange,bitsquare/bitsquare,sakazz/exchange,metabit/bitsquare,metabit/bitsquare,haiqu/bitsquare,bisq-network/exchange,sakazz/exchange,ManfredKarrer/exchange,bitsquare/bitsquare