Get recent pandoc in travis from ppa cran2deb4ubuntu

This ppa:<https://launchpad.net/~marutter/+archive/ubuntu/c2d4u> contain
a backport of pandoc trusty package in precise. It can be used until
travis update his environment to ubuntu 14.04.

.travis.yml

@@ -12,12 +12,10 b' before_install:'
     - sudo rm -rf /dev/shm && sudo ln -s /run/shm /dev/shm
     # Pierre Carrier's PPA for PhantomJS and CasperJS
     - time sudo add-apt-repository -y ppa:pcarrier/ppa
-    - time sudo apt-get update
-    - time sudo apt-get install casperjs libzmq3-dev
     # Needed to get recent version of pandoc in ubntu 12.04
-    - time sudo apt-get install haskell-platform
-    - time cabal update
-    - time cabal install pandoc==1.12.1
+    - time sudo add-apt-repository -y ppa:marutter/c2d4u
+    - time sudo apt-get update
+    - time sudo apt-get install pandoc casperjs libzmq3-dev
     # pin tornado < 4 for js tests while phantom is on super old webkit
     - if [[ $GROUP == 'js' ]]; then pip install 'tornado<4'; fi
     - time pip install -f https://nipy.bic.berkeley.edu/wheelhouse/travis jinja2 sphinx pygments tornado requests!=2.4.2 mock pyzmq jsonschema jsonpointer mistune