Add removal of bang operator (!) to upgrade doc

Author: andys8

upgrade-docs/0.19.md

@@ -91,6 +91,7 @@ Both are quite similar to the `elm-package.json` format, and `elm-upgrade` can h
 - `uncurry`
 - `curry`
 - `flip`
+- `(!)`
 
 Prefer named helper functions in these cases.