Switch to 2.1.2 on Heroku
Add metrics to build API
Use "$@" instead of eval "$@" in travis_retry

eval "$@" will cause issues with commands that have quotes in them,
making `travis_retry ruby -e 'p ARGV'` run the command `ruby -e p ARGV`,
which won't work correctly. Not using `eval` means that some things
won't work right (mostly just `time <command>`, I believe), but this is
the old behaviour that didn't seem to break for anyone.