Tests crash on a newly created project

[seapagan]

Describe the bug
When pytest is run it crashes due to the lack of the greenlet package. This is used for concurrency in the coverage module.

To Reproduce

1. Create a new project
2. run pytest
3. pytest crashes with the exception below:

coverage.exceptions.ConfigError: Couldn't trace with concurrency=greenlet, the module isn't installed.

Expected behaviour

Tests should work!

The fix is to either remove greenlet from the coverage config, or install it as a dev dependency by default. Probably go for the latter