Merge PR #310 into 11.0

Signed-off-by pedrobaeza

.travis.yml

@@ -11,12 +11,7 @@ addons:
       - python-lxml # because pip installation is slow
       - pdftk
       - wkhtmltopdf  # only add if needed and check the before_install section below
-  postgresql: "9.6"
-
-# set up an X server to run wkhtmltopdf.
-before_install:
-  - "export DISPLAY=:99.0"
-  - "sh -e /etc/init.d/xvfb start"
+  postgresql: "9.6" 
 
 language: python