lua-penlight: Update to 1.9.1
## 1.9.1 (2020-09-27)
- fix: dir.walk [#350](https://github.com/lunarmodules/Penlight/pull/350)
## 1.9.1 (2020-09-24)
- released to superseed the 1.9.0 version which was retagged in git after some
distro's already had picked it up. This version is identical to 1.8.1.
## 1.8.1 (2020-09-24) (replacing a briefly released but broken 1.9.0 version)
## Fixes
- In `pl.class`, `_init` can now be inherited from grandparent (or older ancestor) classes. [#289](https://github.com/lunarmodules/Penlight/pull/289)
- Fixes `dir`, `lexer`, and `permute` to no longer use coroutines. [#344](https://github.com/lunarmodules/Penlight/pull/344)
## 1.8.0 (2020-08-05)
### New features
- `pretty.debug` quickly dumps a set of values to stdout for debug purposes
### Changes
- `pretty.write`: now also sorts non-string keys [#319](https://github.com/lunarmodules/Penlight/pull/319)
- `stringx.count` has an extra option to allow overlapping matches
[#326](https://github.com/lunarmodules/Penlight/pull/326)
- added an extra changelog entry for `types.is_empty` on the 1.6.0 changelog, due
to additional fixed behaviour not called out appropriately [#313](https://github.com/lunarmodules/Penlight/pull/313)
- `path.packagepath` now returns a proper error message with names tried if
it fails
### Fixes
- Fix: `stringx.rfind` now properly works with overlapping matches
[#314](https://github.com/lunarmodules/Penlight/pull/314)
- Fix: `package.searchpath` (in module `pl.compat`)
[#328](https://github.com/lunarmodules/Penlight/pull/328)
- Fix: `path.isabs` now reports drive + relative-path as `false`, eg. "c:some/path" (Windows only)
- Fix: OpenResty coroutines, used by `dir.dirtree`, `pl.lexer`, `pl.permute`. If
available the original coroutine functions are now used [#329](https://github.com/lunarmodules/Penlight/pull/329)
- Fix: in `pl.strict` also predefine global `_PROMPT2`
- Fix: in `pl.strict` apply `tostring` to the given name, in case it is not a string.
- Fix: the lexer would not recognize numbers without leading zero; "-.123".
See [#315](https://github.com/lunarmodules/Penlight/issues/315)
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