title: Attached form button doesn't trigger form submit when clicked
body: <p>Consider following example:</p>
  
  <pre><code>import React, { Component } from 'react'
  import { Form } from 'semantic-ui-react'
  
  class FormExample extends Component {
    state = {}
  
    handleChange = (e, { name, value }) =&gt; this.setState({ [name]: value })
  
    handleSubmit = () =&gt; this.setState({ email: '', name: '' })
  
    render() {
      const { name, email } = this.state
  
      return (
        &lt;Form onSubmit={this.handleSubmit}&gt;
          &lt;Form.Group&gt;
            &lt;Form.Input placeholder='Name' name='name' value={name} onChange={this.handleChange} /&gt;
            &lt;Form.Input placeholder='Email' name='email' value={email} onChange={this.handleChange} /&gt;
            &lt;Form.Button attached='bottom' content='Submit' /&gt;
          &lt;/Form.Group&gt;
        &lt;/Form&gt;
      )
    }
  }
  </code></pre>
  
  <p>When <code>Form.Button</code> is attached clicking it does not leads to form submission.  When <code>attached</code> property is omitted <code>onSubmit</code> handler works as expected.</p>
  
  <p>Is it expected behaviour or should I file a bug issue on GitHub?</p>