Make probot/stale more useful (#1086)
Make probot/stale more useful (#1086)

* Make probot/stale more useful

Propose the following changes:
- `daysUntilStale: 60 -> 21`: With 5 track maintainers (3+ active), issues are being manually closed after ~20 days frequently. 60 days is too long.
- Add `epic` to `exemptLabels`: `epic` denotes issues that are usually super-issues, and closing every sub-issue takes a lot of effort and time.
- `staleLabel: on hiatus -> abandoned`: `abandoned` is typically used by the maintainers here, so change for consistency

* ignore "enchancement" and "beginner friendly" labels

jmluy/xpython,pheanex/xpython,exercism/python,smalley/python,behrtam/xpython,smalley/python,jmluy/xpython,N-Parsons/exercism-python,exercism/xpython,N-Parsons/exercism-python,pheanex/xpython,behrtam/xpython,exercism/python,exercism/xpython