message: Fix example register for all rules
  Wrong const is used in doc.
diff: @@ -274,7 +274,7 @@ Or you can globally define all the available rules in the `@vee-validate/rules`
  import { defineRule } from 'vee-validate';
  import AllRules from '@vee-validate/rules';
  -Object.keys(rules).forEach(rule => {
  +Object.keys(AllRules).forEach(rule => {
  defineRule(rule, AllRules[rule]);
  });
  ```
  