Issue title: Validating dynamic form
 Issue body: Hi, 
I am trying to write validations for a dynamic form. While validating the regex on a text field it throws this error "this.options.with.test is not a function" in format.js. The regex that i am trying to validate is /^\d+$/. The following is my code snippet.
`if (wizardStepFields.regExVal !== null) {
                  validationsItem.format = {};
                  validationsItem.format.with = wizardStepFields.regExVal;
                  validationsItem.format.message = "invalid value";

               }`


Here wizardStepFields.regExVal has the value "/^\d+$/"
 Comments: 
 Comment 0: I am going to close this issue for now, feel free to reopen this issue if you feel like it's still relevant and we should take a jarviseric@example.com.
{'source': 'GithubIssues', 'repo_name_with_owner': 'DockYard/ember-validations', 'issue_id': 135436987, 'repo_stars': 123.0}