Added latex packages for travis build (to get the documentation right)

.travis.yml

@@ -20,6 +20,7 @@ before_install:
 - sudo add-apt-repository -y ppa:biometrics/bob
 - sudo apt-get update -qq
 - sudo apt-get install -qq --force-yes libboost-all-dev libblitz1-dev libhdf5-serial-dev libatlas-dev libatlas-base-dev liblapack-dev texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended
+- sudo apt-get install -qq --force-yes dvipng texlive-latex-base texlive-latex-extra texlive-math-extra texlive-latex-recommended texlive-fonts-recommended
 - if [ -n "${NUMPYSPEC}" ]; then sudo apt-get install -qq gfortran; fi
 - if [ -n "${NUMPYSPEC}" ]; then pip install --find-links http://wheels.astropy.org/ --find-links http://wheels2.astropy.org/ --use-wheel numpy$NUMPYSPEC; fi
 - pip install --find-links http://wheels.astropy.org/ --find-links http://wheels2.astropy.org/ --use-wheel sphinx nose==1.3.0 jinja2==2.6 pygments==1.6 cpp-coveralls