HaXml-1.25.7: Changelog.md

## 1.25.7 (2021-10-15)
- many hlint fixes
- fix the rendering of time durations (#1)

## 1.25.6 (2021-09-26)

- GHC 8.8, 8.10, and 9.0 compatibility

## 1.25.5 (2018-10-30)

- GHC-8.4 and GHC-8.6 compatibility
  - Monoids have Semigroup instances