Lint for outdated master

[epruesse]

Currently, below fragment aborts build if the branch is not up to date with master on certain files:

https://github.com/bioconda/bioconda-recipes/blob/232e99747a668355fb2c65217a1418e7d59dd137/.circleci/setup.sh#L23

By turning this into a lint, we can have it pre-checked by the bot driven lint.