Setup travis cron build that syncs the blockchain

Travis support cron job builds, and public repo travis jobs have a maximum run time of 50 minutes. Syncing should take less than that for a while.

We can run a build in a linux container that syncs the blockchain up to 100%. If it does not reach 100% after , consider the build failed.

Note, due to the time limit this solution is not a long term one and we'd be better off with our own machine that continually resynced the blockchain, but such as solution would not integrate with our existing build failure system easily (although possibly a github notification hook could be implemented in our test runner).