Bump pip-tools from 2.0.2 to 3.1.0
Bump pip-tools from 2.0.2 to 3.1.0

Bumps [pip-tools](https://github.com/jazzband/pip-tools) from 2.0.2 to 3.1.0.
- [Release notes](https://github.com/jazzband/pip-tools/releases)
- [Changelog](https://github.com/jazzband/pip-tools/blob/master/CHANGELOG.md)
- [Commits](https://github.com/jazzband/pip-tools/compare/2.0.2...3.1.0)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
ebmdatalab/openprescribing,ebmdatalab/openprescribing,ebmdatalab/openprescribing,ebmdatalab/openprescribing,annapowellsmith/openpresc,annapowellsmith/openpresc,annapowellsmith/openpresc,annapowellsmith/openpresc