2017-08-20 Pandoc on ubuntu and WSL

I was using the Windows Subsystem for Linux to test a module with Linux. I could not make it work due to an old version of pandoc. Surprisingly, the default apt-get install pandoc installed a very old version (1.12). I could not convert any notebook with nbconvert into latex. I finally installed the latest version (1.19) and it worked perfectly. You can see the installation step in file .circleci/config.yml. That was not the last issue because pandoc seems to be very slow on WSL. About that, you can read: massive delay to call pandoc using the Windows Subsystem for Linux (WSL) or Bash for Windows, stack ghc painfully slow.