update test script to stash bench marks somewhere outside the CI instance

[ivoysey]

some choices:

• store in S3 https://docs.travis-ci.com/user/uploading-artifacts/
• push to github pages https://docs.travis-ci.com/user/deployment/pages/
• push back to the same repo https://gist.github.com/willprice/e07efd73fb7f13f917ea
• run SQL somewhere light weight and push there https://docs.travis-ci.com/user/database-setup/
• something else that we could run locally to just store files, like S3 would, but without needing to pay amazon

It would be cool to be able to look at the gas usage of a test over time, paired with commits, so that we could say things like "oh this has been pretty stable but is now a lot more expensive, what went wrong with that optimization?".

S3 seems like a heavy weight thing but maybe it's not; at the volume we'd be at it's basically free but I think I would still need a plan. (https://aws.amazon.com/s3/pricing/). Pushing to pages won't give me the longitudinal data in an easy way, but is pretty light weight. Pushing back to the same repo makes some commit churn, which can be awkward, and doesn't have easy longitudinal data either, but also doesn't have to pretend to be a webpage. SQL is crusty and old but well understood and something we could run locally if we have hardware.