[CI] run travis on trusty & xenial

.travis.yml

@@ -31,6 +31,9 @@ only:
   - debian
   - devel
 matrix:
+  include:
+    - dist: trusty
+    - dist: xenial
 allow_failures:
   - compiler:
 before_install: ./travis_custom/custom_before_install

travis_custom/custom_before_install

@@ -6,7 +6,7 @@ set -x
 set -v
 
 # Add robotpkg
-sudo sh -c "echo \"deb [arch=amd64] http://robotpkg.openrobots.org/packages/debian/pub xenial robotpkg\" >> /etc/apt/sources.list "
+sudo sh -c "echo \"deb [arch=amd64] http://robotpkg.openrobots.org/packages/debian/pub $(lsb_release -cs) robotpkg\" >> /etc/apt/sources.list "
 curl http://robotpkg.openrobots.org/packages/debian/robotpkg.key | sudo apt-key add -
 
 # show memory usage before install