message: CI: make melodic mandatory and indigo optional
diff: sudo: required
  -dist: trusty
  +dist: xenial
  language: generic
  notifications:
  email:
  @@ -17,8 +17,8 @@ env:
  - ROS_DISTRO=melodic UPSTREAM_WORKSPACE=debian
  matrix:
  allow_failures:
  - - env: ROS_DISTRO=melodic UPSTREAM_WORKSPACE=file
  - - env: ROS_DISTRO=melodic UPSTREAM_WORKSPACE=debian
  + - env: ROS_DISTRO=indigo UPSTREAM_WORKSPACE=file
  + - env: ROS_DISTRO=indigo UPSTREAM_WORKSPACE=debian
  install:
  - git clone https://github.com/ros-industrial/industrial_ci.git .ci_config
  script:
  