Adds missing comma

Author: fxn

activerecord/CHANGELOG.md

@@ -37,7 +37,7 @@
 
 *   Remove warning message when running SQLite in production, but leave it unconfigured.
 
-    There are valid use cases for running SQLite in production. However it must be done
+    There are valid use cases for running SQLite in production. However, it must be done
     with care, so instead of a warning most users won't see anyway, it's preferable to
     leave the configuration commented out to force them to think about having the database
     on a persistent volume etc.