Add pre-release builds to CI matrix

Author: wxmerkt

.travis.yml

@@ -13,6 +13,12 @@ env:
   matrix:
     - ROS_REPOSITORY_PATH=http://packages.ros.org/ros/ubuntu
     - ROS_REPOSITORY_PATH=http://packages.ros.org/ros-shadow-fixed/ubuntu
+    - ROS_DISTRO="kinetic" PRERELEASE=true
+    - ROS_DISTRO="melodic" PRERELEASE=true
+matrix:
+  allow_failures:
+    - env: ROS_DISTRO="kinetic" PRERELEASE=true
+    - env: ROS_DISTRO="melodic" PRERELEASE=true
 install:
   - git clone https://github.com/ros-industrial/industrial_ci.git .ci_config
 script: