fix changelog typo (#35)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b8fb9b0..1bfa9c3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 1.3.1-nullsafety.1
+## 1.3.0-nullsafety.1
 
 * Allow the <=2.9.10 stable sdks.