changelog: make order of change types match keepachangelog.com

Author: jonasnick

CHANGELOG.md

@@ -6,16 +6,16 @@ Each change falls into one of the following categories: Added, Changed, Deprecat
 
 ## [Unreleased]
 
+### Added
+ - Added `secp256k1_selftest`, to be used in conjunction with `secp256k1_context_static`.
+
 ### Changed
  - Enable modules schnorrsig, extrakeys and ECDH by default in ./configure
 
 ### Deprecated
  - Deprecated context flags `SECP256K1_CONTEXT_VERIFY` and `SECP256K1_CONTEXT_SIGN`. Use `SECP256K1_CONTEXT_NONE` instead.
  - Renamed `secp256k1_context_no_precomp` to `secp256k1_context_static`.
 
-### Added
- - Added `secp256k1_selftest`, to be used in conjunction with `secp256k1_context_static`.
-
 ## [MAJOR.MINOR.PATCH] - YYYY-MM-DD
 
 ### Added/Changed/Deprecated/Removed/Fixed/Security