Revert "Move to container based Travis"

This reverts commit a006498281.

SWE-GLib cannot use container based tests, as the gnome-common package
is disallowed.

Issue travis-ci/apt-package-whitelist#1103 has been opened to resolve
this dependency.

.travis.yml

@@ -1,11 +1,6 @@
-sudo: false
 language: c
-addons:
+before_install: sudo apt-get update
-  apt:
+install: sudo apt-get install libglib2.0-dev gobject-introspection gnome-common
-    packages:
-    - libglib2.0-dev
-    - gobject-introspection
-    - gnome-common
 before_script: ./autogen.sh
 script:
   - make