Upgrade travis to container-based infrastructure

Author: samueltardieu

.travis.yml

@@ -1,5 +1,9 @@
 language: c
-before_install:
-    - sudo apt-get update -qq
-    - sudo apt-get install gforth texinfo texlive
+sudo: false
+addons:
+  apt:
+    packages:
+      - gforth
+      - texinfo
+      - texlive
 script: make test