[smuxi: 122/179] Travis-CI: add PPA for GTK# 2.12.40 backport

[Mirco M. M. Bauer <mmmbauer src gnome org>]

commit 46bdc855f83213db8948ff5400ac989b7ec8bf52
Author: Mirco Bauer <meebey meebey net>
Date:   Mon Jan 9 16:32:15 2017 +0800

    Travis-CI: add PPA for GTK# 2.12.40 backport
    
    As Smuxi is using the GtkBuilder API of GTK#, we now need to install the GTK#
    2.12.40 backport from the smuxi-daily PPA to fulfill the build requirement.

 .travis.yml |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/.travis.yml b/.travis.yml
index 785a3ff..8269684 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -13,6 +13,11 @@ mono:
     - 3.2.8
     - 2.10.8
 
+addons:
+    apt:
+        sources:
+        - sourceline: 'ppa:meebey/smuxi-daily'
+
 install:
     - sudo apt-get update > /dev/null
     - sudo apt-get build-dep smuxi > /dev/null