add some latex dependencies

.travis.yml

@@ -3,7 +3,7 @@ language: java
 before_install:
   - sudo apt-get -qq update
   - sudo apt-get install -y python-imaging rubber
-  - sudo apt-get install -y texlive-base
+  - sudo apt-get install -y dvipng texlive-math-extra
   - rvm install 2.0.0
   - gem install travis-custom-deploy
 install: