Update .travis.yml

Author: markusgft

.travis.yml

@@ -7,15 +7,19 @@ services:
 language: c++
 compiler:
   - clang
+cache:
+  directories:
+  - $HOME/.ccache
 notifications:
   email:
     recipients:
       - markusgft@gmail.com
 env:
+  global:
+    - CCACHE_DIR=$HOME/.ccache # enables C/C++ caching
   matrix:
-    - ROS_DISTRO="kinetic"  ROS_REPOSITORY_PATH=http://packages.ros.org/ros/ubuntu NOT_TEST_INSTALL=true
-    - ROS_DISTRO="kinetic"  ROS_REPOSITORY_PATH=http://packages.ros.org/ros-shadow-fixed/ubuntu NOT_TEST_INSTALL=true
-    - ROS_DISTRO="kinetic"  PRERELEASE=true
+    - ROS_DISTRO="kinetic"
+    - ROS_DISTRO="melodic"
 matrix:
   allow_failures:
     - env: ROS_DISTRO="kinetic"  PRERELEASE=true