Update pre-install instructions with libav components

.travis.yml

@@ -16,7 +16,7 @@ before_install:
   - sudo add-apt-repository -y ppa:biometrics/bob
   - sudo add-apt-repository -y ppa:biometrics/bob.preview
   - sudo apt-get update -qq
-  - sudo apt-get install -qq --force-yes bob-dev libmatio-dev
+  - sudo apt-get install -qq --force-yes bob-dev libavcodec-dev libavformat-dev libswscale-dev
   - if [ -n "${NUMPYSPEC}" ]; then sudo apt-get install -qq libatlas-dev libatlas-base-dev liblapack-dev gfortran; fi
   - if [ -n "${NUMPYSPEC}" ]; then pip install --upgrade pip setuptools; fi
   - if [ -n "${NUMPYSPEC}" ]; then pip install --find-links http://wheels.astropy.org/ --find-links http://wheels2.astropy.org/ --use-wheel numpy$NUMPYSPEC sphinx nose; fi