React Formik use submitForm outside <Formik /> : <h2>Current Behavior</h2>

<pre><code>&lt;Formik
    isInitialValid
    initialValues={{ first_name: 'Test', email: 'test@mail.com' }}
    validate={validate}
    ref={node =&gt; (this.form = node)}
    onSubmitCallback={this.onSubmitCallback}
    render={formProps =&gt; {
        const fieldProps = { formProps, margin: 'normal', fullWidth: true, };
        const {values} = formProps;
        return (
            &lt;Fragment&gt;
                &lt;form noValidate&gt;
                    &lt;TextField
                        {...fieldProps}
                        required
                        autoFocus
                        value={values.first_name}
                        type="text"
                        name="first_name"

                    /&gt;

                    &lt;TextField
                        {...fieldProps}
                        name="last_name"
                        type="text"
                    /&gt;

                    &lt;TextField
                        {...fieldProps}
                        required
                        name="email"
                        type="email"
                        value={values.email}

                    /&gt;
                &lt;/form&gt;
                &lt;Button onClick={this.onClick}&gt;Login&lt;/Button&gt;
            &lt;/Fragment&gt;
        );
    }}
/&gt;
</code></pre>

<p>I'm trying this solution <a href="https://github.com/jaredpalmer/formik/issues/73#issuecomment-317169770" rel="noreferrer">https://github.com/jaredpalmer/formik/issues/73#issuecomment-317169770</a> but it always return me <code>Uncaught TypeError: _this.props.onSubmit is not a function</code></p>

<p>When I tried to <code>console.log(this.form)</code> there is <code>submitForm</code> function.</p>

<p>Any solution guys?</p>

<hr>

<p>
- Formik Version: latest
- React Version: v16
- OS:  Mac OS</p>
