README.md: Add GitHub Actions and Travis CI badges
README.md: Add GitHub Actions and Travis CI badges

Badges? We got your stinkin’ badges!

yenliangl/bitcoinj,bitcoinj/bitcoinj,natzei/bitcoinj,peterdettman/bitcoinj,peterdettman/bitcoinj,yenliangl/bitcoinj,bitcoinj/bitcoinj,natzei/bitcoinj