clean-up Travis CI config (#438)

.travis.yml

-sudo: required
-dist: trusty
 language: generic
-compiler:
-  - gcc
+services:
+  - docker
+
 notifications:
   email:
     on_success: always
     on_failure: always
 env:
   matrix:
-    - USE_DEB=true  ROS_DISTRO="kinetic"   ROS_REPOSITORY_PATH=http://packages.ros.org/ros/ubuntu
-    - USE_DEB=true  ROS_DISTRO="kinetic"   ROS_REPOSITORY_PATH=http://packages.ros.org/ros-shadow-fixed/ubuntu
-    - USE_DEB=true  ROS_DISTRO="kinetic"   PRERELEASE=true
-    - USE_DEB=true  ROS_DISTRO="melodic"   ROS_REPOSITORY_PATH=http://packages.ros.org/ros/ubuntu
-    - USE_DEB=true  ROS_DISTRO="melodic"   ROS_REPOSITORY_PATH=http://packages.ros.org/ros-shadow-fixed/ubuntu
-    - USE_DEB=true  ROS_DISTRO="melodic"   PRERELEASE=true
+    - ROS_DISTRO="kinetic"   ROS_REPO=ros
+    - ROS_DISTRO="kinetic"   ROS_REPO=ros-shadow-fixed
+    - ROS_DISTRO="kinetic"   PRERELEASE=true
+    - ROS_DISTRO="melodic"   ROS_REPO=ros
+    - ROS_DISTRO="melodic"   ROS_REPO=ros-shadow-fixed
+    - ROS_DISTRO="melodic"   PRERELEASE=true
 matrix:
   allow_failures:
-    - env: USE_DEB=true  ROS_DISTRO="melodic"   ROS_REPOSITORY_PATH=http://packages.ros.org/ros/ubuntu
-    - env: USE_DEB=true  ROS_DISTRO="melodic"   ROS_REPOSITORY_PATH=http://packages.ros.org/ros-shadow-fixed/ubuntu
-    - env: USE_DEB=true  ROS_DISTRO="melodic"   PRERELEASE=true
+    - env: ROS_DISTRO="melodic"   ROS_REPO=ros
+    - env: ROS_DISTRO="melodic"   ROS_REPO=ros-shadow-fixed
+    - env: ROS_DISTRO="melodic"   PRERELEASE=true
 install:
-  - git clone https://github.com/ros-industrial/industrial_ci.git .ci_config
+  - git clone --quiet --depth=1 https://github.com/ros-industrial/industrial_ci.git .ci_config
 script:
   - source .ci_config/travis.sh