.gitlab-ci.yml: Add basic configuration for GitLab continuous integration.
.gitlab-ci.yml: Add basic configuration for GitLab continuous integration.

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