Fix travis configuration

.travis.yml

@@ -1,13 +1,19 @@
 sudo: false
-cache: pip
+language: python
+
+cache:
+  apt: true
+  directories:
+    - $HOME/.cache/pip
 
 addons:
   apt:
     packages:
       - expect-dev  # provides unbuffer utility
       - python-lxml # because pip installation is slow
-
-language: python
+      - python-simplejson
+      - python-serial
+      - python-yaml
 
 python:
   - '2.7'
@@ -21,7 +27,7 @@ env:
   - TESTS="1" ODOO_REPO="odoo/odoo"
   - TESTS="1" ODOO_REPO="OCA/OCB"
   global:
-  - VERSION="9.0"
+  - VERSION="9.0" LINT_CHECK="0" TESTS="0"
 
 install:
   - git clone --depth=1 https://github.com/OCA/maintainer-quality-tools.git ${HOME}/maintainer-quality-tools