Update protobuf-gradle-plugin to 0.8.6.
Update protobuf-gradle-plugin to 0.8.6.

yenliangl/bitcoinj,peterdettman/bitcoinj,schildbach/bitcoinj,peterdettman/bitcoinj,GroestlCoin/groestlcoinj,bitcoinj/bitcoinj,GroestlCoin/groestlcoinj,kmels/bitcoinj,natzei/bitcoinj,yenliangl/bitcoinj,kmels/bitcoinj,GroestlCoin/groestlcoinj,natzei/bitcoinj,schildbach/bitcoinj,bitcoinj/bitcoinj