Update .travis.yml and enable wkhtml2pdf (#75)

Update .travis.yml and enable wkhtml2pdf

.travis.yml

@@ -1,27 +1,41 @@
 language: python
+sudo: false
+cache:
+  apt: true
+  directories:
+    - $HOME/.cache/pip
 
 python:
   - "2.7"
 
-sudo: false
-cache: pip
-
 addons:
   apt:
+    sources:
+      - pov-wkhtmltopdf
     packages:
       - expect-dev  # provides unbuffer utility
       - python-lxml  # because pip installation is slow
+      - python-simplejson
+      - python-serial
+      - python-yaml
+      - wkhtmltopdf  # only add if needed and check the before_install section below
+
+# set up an X server to run wkhtmltopdf.
+before_install:
+  - "export DISPLAY=:99.0"
+  - "sh -e /etc/init.d/xvfb start"
 
 env:
   global:
   - VERSION="8.0" TESTS="0" LINT_CHECK="0" TRANSIFEX="0"
   - TRANSIFEX_USER='transbot@odoo-community.org'
   - secure: "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"
+
   matrix:
   - LINT_CHECK="1"
-  - TRANSIFEX="1"
   - TESTS="1" ODOO_REPO="odoo/odoo"
   - TESTS="1" ODOO_REPO="OCA/OCB"
+  - TRANSIFEX="1"
 
 virtualenv:
   system_site_packages: true