Keep the PDFs updated during build process

[lsaether]

Using Travis CI it should be possible to build the pdf from the .tex souce on every commit to master branch and pop up the updated pdf on a publicly accessible link such as grandpa.web3.foundation. Right now I see that there's a hanging PR from March of someone updating the pdf. Implementing something like this in the build process would ensure it's always kept up to date and no one would have to worry about updating it manually.