pyupgrade @ 3.7

[tony]

pip install pyupgrade autoflake; \
pyupgrade --py37 tests/**/*.py docs/**/*.py libtmux/**/*.py; \
poetry run autoflake tests/**/*.py docs/**/*.py libtmux/**/*.py -i --ignore-init-module-imports; \
make black isort

[codecov]

Codecov Report

Merging #357 (6589275) into master (ae6e07f) will decrease coverage by 0.02%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master     #357      +/-   ##
==========================================
- Coverage   87.82%   87.80%   -0.03%     
==========================================
  Files          15       15              
  Lines        1511     1500      -11     
==========================================
- Hits         1327     1317      -10     
+ Misses        184      183       -1     

Impacted Files	Coverage Δ
libtmux/exc.py	100.00% <ø> (ø)
libtmux/pane.py	82.35% <ø> (ø)
tests/conftest.py	86.95% <ø> (+1.85%)	⬆️
libtmux/common.py	86.86% <66.66%> (-0.07%)	⬇️
libtmux/server.py	79.31% <71.42%> (ø)
libtmux/session.py	81.43% <100.00%> (-0.12%)	⬇️
libtmux/test.py	42.85% <100.00%> (ø)
libtmux/window.py	84.33% <100.00%> (ø)
tests/test_common.py	98.26% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ae6e07f...6589275. Read the comment docs.