Switch all update workflows to `pipenv lock/sync`
Switch all update workflows to `pipenv lock/sync`

- `pipenv update` currently doesn't actually run `pipenv lock`
- Semantics around this changed but it doesn't look like the code did
- `pipenv update` should operate similarly for all operations by running
`lock` followed by `sync`
- Fixes #2179

Signed-off-by: Dan Ryan <2591e5f46f28d303f9dc027d475a5c60d8dea17a@danryan.co>

kennethreitz/pipenv