Sync base/changelog.md

This updates the base-4.10.0.0 entry heading which has diverged from

 http://hackage.haskell.org/package/base-4.10.0.0/src/changelog.md

and while at it also sets the GHC version for the base-4.11 entry to
avoid confusion about what GHC 8.2.2's base is going to include.

[skip ci]