Travis: Lets actually use the PPA

Author: JelteF

.travis.yml

@@ -3,7 +3,7 @@ python:
     - '3.3'
     - '3.4'
 before_install:
-    - sudo add-apt-repository ppa:texlive-backports/ppa
+    - sudo add-apt-repository ppa:texlive-backports/ppa -y
     - sudo apt-get update
 install:
     - sudo apt-get install texlive-latex-extra texlive-pictures