clean up our environment in the binstub

[michaelglass]

another approach for #1

should outfox rails#626

paired with @BrianHicks

when we have a big environment, we sometimes get "argument list too long errors"

how to repro:

1. add a really long environmental variable prefixed with NIX_
2. in one terminal, run spring server (so you can easily see debug info, there's another way but you have to read the docs for that one)
3. in another terminal run, rails c

without this binstub: argument errors!!!
with this binstub: no errors, your life is a good life full of meaning

[BrianHicks]

works fine for me too! 🎉

[michaelglass]

@asterite can you release this as a new version?

[asterite]

Sure! And I'll send a PR to the monolith with the new version.