py-isort: updated to 4.3.10

4.3.10:
- Fixed Windows incompatibilities
- Fixed relative import sorting bug
- Fixed "no_lines_before" to also be respected from previous empty sections.
- Fixed slow-down introduced by finders mechanism by adding a LRU cache
- Fixed issue 842 default encoding not-set in Python2
- Restored Windows automated testing
- Added Mac automated testing

(adam)