```
net-im/py-slackclient: Update to 2.7.1
- Update to 2.7.1 [1][2]
- Remove pytest-runner dependency (only required for setup.py test command [3])
- Add ca_root_nss to TEST_DEPENDS (tests access https://slack.com/)
- Update MAINTAINER
[1] https://github.com/slackapi/python-slackclient/releases
[2] https://github.com/slackapi/python-slackclient/releases?after=v2.3.1
[3] To upstream: conditionalise dependency to setup.py test command
Approved by: koobs (maintainer)
Differential_Revision: D25275
```