Bump version: 0.8.9 → 0.9.0 #179

Job	Run time
lint (3.11)	41s
conf_pip_py27	2m 52s
conf_pip_py36 (3.11)	2m 2s
ConfPip (3.13)	32s
ConfPip (3.14)	33s
ConfPip (3.9)	37s
set_pip_mirror (macOS-latest)	2m 14s
set_pip_mirror (windows-latest)	1m 24s
	10m 55s

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