[pygobject] docs: update travis-ci example to Ubuntu xenial

[Christoph Reiter <creiter src gnome org>]

commit 2beb49cf2501063d9f19bc86ba4c0a688808612d
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Fri Feb 15 15:41:35 2019 +0100

    docs: update travis-ci example to Ubuntu xenial
    
    Real changes here: https://github.com/pygobject/pygobject-travis-ci-examples/commit/6a462f528
    This gives us a newer gtk/pygobject so update the version info in the docs.

 docs/guide/testing.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/docs/guide/testing.rst b/docs/guide/testing.rst
index b4493e86..cae4fc7f 100644
--- a/docs/guide/testing.rst
+++ b/docs/guide/testing.rst
@@ -16,8 +16,8 @@ creates a temporary X server without the need for any real display hardware.
 Continuous Integration using Travis CI / CircleCI
 -------------------------------------------------
 
-Travis CI uses a rather old Ubuntu and thus the supported GTK is at 3.10 and
-PyGObject is at 3.12. If that's enough for you then have a look at our Travis
+Travis CI uses a rather old Ubuntu and thus the supported GTK is at 3.18 and
+PyGObject is at 3.20. If that's enough for you then have a look at our Travis
 CI example project:
 
     |github-logo| https://github.com/pygobject/pygobject-travis-ci-examples