Use language: generic to use the minimal image

Since we are pulling all dependencies from PPA this just gives use the
advantage of faster boot up times.

.travis.yml

@@ -1,4 +1,9 @@
-language: cpp
+#language: cpp
+# This makes travis use the thin image which boots faster
+language: generic
+
+
+# sudo:required is needed for trusty images
 sudo: required
 dist: trusty