title: axios catch doesn't catch error
body: <p>I'm using <code>axios 0.17.0</code> with the following code:</p>
  
  <pre><code>this.props.userSignupRequest(this.state)
    .then( res =&gt; { console.log(res.data) } )
    .catch( err =&gt; { this.setState({ errors: err.response }) } )
  </code></pre>
  
  <p>And the server is set to return a <code>400</code> when user signup validation doesn't pass. That also shows up in console: <code>POST 400 (Bad Request)</code>, but the <code>setState</code> is not being executed. Why is that? I also tried <code>console.log(err)</code> and nothing.</p>