v1.8.2

Fixes

• Fix global configuration not inherited correctly in scale-out command of tiup-cluster (#1701, @srstack)
• Fix errors starting tiup-playground in some circumstances (#1712 #1715, @nexustar)
• Fix error comparing nightly versions in tiup-cluster (#1702, @srstack)

Improvements

• Update out-of-date documents of tiup mirror (#1705, @dveeden)