message: add colored echos
diff: #!/usr/bin/env bash
  +YELLOW='\033[0;33m'
  +NC='\033[0m'
  +echo
  +echo "+++ Run docker build and publish. +++"
  +echo
  if [ "$TRAVIS_BRANCH" == "master" ] || [ "$TRAVIS_BRANCH" == "develop" ]; then
  if [ "$TRAVIS_PULL_REQUEST" == "false" ]; then
  echo "build docker images";
  @@ -15,8 +20,8 @@ if [ "$TRAVIS_BRANCH" == "master" ] || [ "$TRAVIS_BRANCH" == "develop" ]; then
  docker push hdafbi/geli-web-frontend;
  docker push hdafbi/geli-web-frontend:$TRAVIS_BRANCH;
  else
  - echo "omit docker build and publish. (pull request: #$TRAVIS_PULL_REQUEST)";
  + echo -e "${YELLOW}+ WARNING: pull request #$TRAVIS_PULL_REQUEST -> skipping docker build and publish${NC}";
  fi
  else
  - echo "omit docker build and publish. (wrong branch: $TRAVIS_BRANCH)";
  + echo -e "${YELLOW}+ WARNING: branch $TRAVIS_BRANCH is not whitelisted -> skipping docker build and publish${NC}";
  fi
  