[template-glib] travis: add apt-get update

[Christian Hergert <chergert src gnome org>]

commit 759dbbc11114b68fc6b401c2ba9d66dc2542ff6a
Author: Christian Hergert <christian hergert me>
Date:   Thu Jan 21 12:50:21 2016 -0800

    travis: add apt-get update

 .travis.yml |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/.travis.yml b/.travis.yml
index 4e0322c..3ec6538 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -19,6 +19,7 @@ notifications:
     on_failure: always
 
 before_install:
+  - sudo apt-get update
   - sudo apt-get install libglib2.0-dev libgirepository1.0-dev
 
 install: