Quiet tox warning about `make` being an unrecognized command
Quiet tox warning about `make` being an unrecognized command

We use `make` as part of the tox build, but tox tries to check that any
commands are included in requirements files. For external tools like
`make` you just have to tell tox it's external to avoid the warnings.
For more information see:
https://tox.wiki/en/latest/example/basic.html#allowing-non-virtualenv-commands

Resolves 44

chapel-lang/sphinxcontrib-chapeldomain