Fix #unix_ms to #to_unix_ms in CHANGELOG.md (#7024)

The CHANGELOG for 0.27.0 shows that some instance method names are changed in Time class.

> - **(breaking-change)** Rename `Time#epoch` to `Time#to_unix`. Also `#epoch_ms` to `#to_unix_ms`, and `#epoch_f` to `#to_unix_f`. ([#6662](#6662), thanks @straight-shoota)

Actually, `#epoch_ms` was renamed to `#to_unix_ms`, not `#unix_ms`.

CHANGELOG.md

@@ -61,7 +61,7 @@
 
 ### Time
 
-- **(breaking-change)** Rename `Time#epoch` to `Time#to_unix`. Also `#epoch_ms` to `#unix_ms`, and `#epoch_f` to `#to_unix_f`. ([#6662](https://github.com/crystal-lang/crystal/pull/6662), thanks @straight-shoota)
+- **(breaking-change)** Rename `Time#epoch` to `Time#to_unix`. Also `#epoch_ms` to `#to_unix_ms`, and `#epoch_f` to `#to_unix_f`. ([#6662](https://github.com/crystal-lang/crystal/pull/6662), thanks @straight-shoota)
 - Fixed spec for `Time::Location.load_local` with `TZ=nil`. ([#6740](https://github.com/crystal-lang/crystal/pull/6740), thanks @straight-shoota)
 - Add support for ISO calendar week to `Time`. ([#6681](https://github.com/crystal-lang/crystal/pull/6681), thanks @straight-shoota)
 - Add `Time::Format` support for `%G`, `%g`, `%V`. ([#6681](https://github.com/crystal-lang/crystal/pull/6681), thanks @straight-shoota)