updated .travis.yml

Author: pichillilorenzo

.travis.yml

@@ -16,6 +16,7 @@ before_install:
     - if [ "$TRAVIS_OS_NAME" == "linux"  ]; then
             export DISPLAY=:99.0;
             sh -e /etc/init.d/xvfb start;
+            xvfb -screen 0 1024x768x24 +extension RANDR;
       fi
 
 install: