Min and MaxLength validation of TextArea do nothing

[VincentKeltjens]

Setting the values for MinLength and MaxLength do no appear to trigger the invalid state of a TextArea.

Copied from http://formio.github.io/ngFormBuilder/ and added (which is also broken by the way, but not sure if there should be an issue for this...)

{ input: true, tableView: true, label: "Message", key: "message", placeholder: "What do you think?", prefix: "", suffix: "", rows: 3, multiple: false, defaultValue: "", protected: false, persistent: true, -validate: { required: false, minLength: "10", maxLength: "25", pattern: "", custom: "" }, type: "textarea", -conditional: { show: false, when: null, eq: "" }, $$hashKey: "object:21", autofocus: false, hidden: false, wysiwyg: false, clearOnHide: true, spellcheck: true }