[release] 3.9.1

[release] 3.9.0

[release] 3.8.1

update to webpack4 (PanJiaChen#889)

[release] 3.7.3

[release] 3.7.2

[release] 3.7.1

[release] 3.7.0

[release] 3.6.6

[release] 3.6.5