doc: sort changelog entries for upcoming 0.9.0

I want to keep the same ordering in a future. Looked at the
keepachangelog.com and hold the Added-Changed-Fixed order.

Author: Totktonada

CHANGELOG.md

@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+* `crud.len()` function to calculate the number of tuples
+  in the space for memtx engine and calculate the maximum
+  approximate number of tuples in the space for vinyl engine.
+* Testing: added integration with service coveralls.io (PR #195).
+* Testing: added integration with luacov that allows to generate report with
+  code coverage statistics (PR #195).
+
 ### Changed
 
 * Names of errors generated by CRUD operations have been unified (PR #184).
@@ -20,15 +29,6 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 * Damaging of opts table by CRUD methods (#192).
 * Ignoring of `bucket_id` option in `crud.select()`/`crud.pairs()` (#220).
 
-### Added
-
-* `crud.len()` function to calculate the number of tuples
-  in the space for memtx engine and calculate the maximum
-  approximate number of tuples in the space for vinyl engine.
-* Testing: added integration with service coveralls.io (PR #195).
-* Testing: added integration with luacov that allows to generate report with
-  code coverage statistics (PR #195).
-
 ## [0.8.0] - 02-07-21
 
 ### Fixed