[docs] Update Changelog

[oliviertassinari]

• Update the changelog. Closes Could not find changes in CHANGELOG.md for 3.9.3 version #15563
• Fix the v4-alpha wording
• material-ui-pickers has moved to @material-ui/pickers

[mui-pr-bot]

Details of bundle changes.

Comparing: e507497...d8711d2

bundle	parsed diff	gzip diff	prev parsed	current parsed	prev gzip	current gzip
@material-ui/core	+0.08% 🔺	+0.07% 🔺	310,611	310,852	84,595	84,650
@material-ui/core/Paper	+0.12% 🔺	+0.08% 🔺	67,705	67,788	20,130	20,146
@material-ui/core/Paper.esm	+0.14% 🔺	+0.09% 🔺	61,003	61,086	19,038	19,055
@material-ui/core/Popper	+0.55% 🔺	+0.41% 🔺	28,590	28,748	10,290	10,332
@material-ui/core/Textarea	0.00%	0.00%	5,513	5,513	2,381	2,381
@material-ui/core/TrapFocus	0.00%	0.00%	3,780	3,780	1,577	1,577
@material-ui/core/styles/createMuiTheme	0.00%	0.00%	15,943	15,943	5,777	5,777
@material-ui/core/useMediaQuery	0.00%	0.00%	2,106	2,106	977	977
@material-ui/lab	+0.17% 🔺	+0.13% 🔺	139,625	139,866	42,535	42,592
@material-ui/styles	+0.16% 🔺	+0.11% 🔺	51,234	51,317	15,156	15,172
@material-ui/system	0.00%	0.00%	11,765	11,765	3,924	3,924
Button	+0.10% 🔺	+0.07% 🔺	85,318	85,401	25,686	25,704
Modal	0.00%	0.00%	20,366	20,366	6,692	6,692
colorManipulator	0.00%	0.00%	3,904	3,904	1,543	1,543
docs.landing	0.00%	0.00%	51,531	51,531	11,368	11,368
docs.main	+0.54% 🔺	+0.65% 🔺	648,808	652,303	202,575	203,890
packages/material-ui/build/umd/material-ui.production.min.js	+0.08% 🔺	+0.06% 🔺	292,314	292,556	82,476	82,526

Generated by 🚫 dangerJS against d8711d2

[mui-pr-bot]

No bundle size changes comparing 0912310...606b788

Generated by 🚫 dangerJS against 606b788

[eps1lon]

This is still a bad idea with the current yarn version. It adds a lot of duplicate dependencies.

[oliviertassinari]

I have reverted the second commit. It seems that I'm stuck. I can't upgrade the dependencies. If I rm yarn.lock it fails everywhere. if I do it incrementally, we duplicate the dependencies.