isort: Update config for 5.0

See also: https://timothycrosley.github.io/isort/docs/upgrade_guides/5.0.0/

Author: tony

setup.cfg

@@ -50,7 +50,5 @@ include_trailing_comma = true
 multi_line_output = 3
 known_pytest = pytest,py
 known_first_party = libtmux,tmuxp
-split_before_closing_bracket = true
 sections = FUTURE,STDLIB,PYTEST,THIRDPARTY,FIRSTPARTY,LOCALFOLDER
 line_length = 88
-not_skip = __init__.py