fix(validatable): revalidate on rules change (#4640)

* fix(validatable): revalidate on rules change

fixes #4635

* style: remove unused params

Author: jacekkarczmarczyk

src/mixins/validatable.js

@@ -113,11 +113,7 @@ export default {
 
   watch: {
     rules: {
-      handler (newVal, oldVal) {
-        // TODO: This handler seems to trigger when input changes, even though
-        // rules array stays the same? Solved it like this for now
-        if (newVal.length === oldVal.length) return
-
+      handler () {
         this.validate()
       },
       deep: true