[ffigen] docs(changelog): remove extra # (#377)

Remove extra # to produce correct level 1 heading.

pkgs/ffigen/CHANGELOG.md

diff --git a/pkgs/ffigen/CHANGELOG.md b/pkgs/ffigen/CHANGELOG.md
index 6cae5fb..e5aee18 100644
--- a/pkgs/ffigen/CHANGELOG.md
+++ b/pkgs/ffigen/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 5.0.0
+# 5.0.0
 
 - Stable release targeting Dart 2.17, supporting ABI-specific integer types.
 - _EXPERIMENTAL_ support for ObjectiveC on MacOS hosts. The API and output