Update .travis.yml
Update .travis.yml

The travis build is often blocked by the following error

  $ sudo apt-get install -y build-essential
  E: Could not get lock /var/lib/dpkg/lock - open (11: Resource
temporarily unavailable)

Feedback from travis is the dpkg lock file might be locked by an
unattended `apt-get` call that's running in the background on a daily
basis and travis suggests adding the corresponding snippet before
apt-get call in .travis.yml

Signed-off-by: Haihao Xiang <8d677183e5993577d4fa73a419b76987913292d6@intel.com>

01org/libva-cros,01org/libva-cros,01org/libva-cros