[#7] Add line to update aptitude repo

Author: meatballs

.travis.yml

@@ -5,6 +5,7 @@ python:
 before_install:
   - export DISPLAY=:99.0
   - sh -e /etc/init.d/xvfb start
+  - sudo apt-get -qq update
   - sudo apt-get install gfortran
 install:
   - pip install -r requirements.txt