Add dependency to xfonts-75dpi in .travis.yml

.travis.yml

@@ -19,6 +19,7 @@ virtualenv:
 install:
   - git clone https://github.com/OCA/reporting-engine ${HOME}/reporting-engine -b ${VERSION}
   - git clone https://github.com/OCA/maintainer-quality-tools.git ${HOME}/maintainer-quality-tools
+  - sudo apt-get install xfonts-75dpi
   - sudo wget http://sourceforge.net/projects/wkhtmltopdf/files/0.12.2.1/wkhtmltox-0.12.2.1_linux-precise-amd64.deb -P /tmp/
   - sudo dpkg -i /tmp/wkhtmltox-0.12.2.1_linux-precise-amd64.deb
   - export PATH=${HOME}/maintainer-quality-tools/travis:${PATH}