CHANGELOG.md in strong_migrations-0.6.7 vs CHANGELOG.md in strong_migrations-0.6.8

@@ -1,4 +1,8 @@
+## 0.6.8 (2020-05-13)
+
+- `change_column_null` on a column with a `NOT NULL` constraint is safe in Postgres 12+
+
 ## 0.6.7 (2020-05-13)
 
 - Improved comments in initializer
 - Fixed string timeouts for Postgres