const ENV = {
  // ...
  "ember-validated-form": {
    label: {
      submit: "Go for it!"
    },
    css: {
      // bootstrap classes
      group: "form-group",
      radio: "radio",
      control: "form-control",
      label: "col-form-label",
      help: "small form-text text-danger",
      hint: "small form-text text-muted",
      checkbox: "checkbox",
      button: "btn btn-default",
      submit: "btn btn-primary",
      loading: "loading",
      valid: "is-valid",
      invalid: "is-invalid"
    }
  }
  // ...
};

const ENV = {
  // ...
  "ember-validated-form": {
    label: {
      submit: "Go for it!"
    },
    css: {
      // bootstrap classes
      group: "form-group",
      radio: "radio",
      control: "form-control",
      label: "col-form-label",
      help: "small form-text text-danger",
      hint: "small form-text text-muted",
      checkbox: "checkbox",
      button: "btn btn-default",
      submit: "btn btn-primary",
      loading: "loading",
      valid: "is-valid",
      error: "is-invalid"
    }
  }
  // ...
};

Update bootstrap 4 config error class
Update bootstrap 4 config error class

The error class used in `error`, not `invalid`.