title: Flutter Stepper horizontal type not working
body: <p>I have a problem with changing the Stepper type from vertical to horizontal.</p>
  
  <p>This is my code:</p>
  
  <pre><code>body: new ListView.builder(
      itemCount: data == null ? 0 : 5,
      itemBuilder: (BuildContext context, int index) {
        return new Card(
            //child: new Text(data[index]["title"]),
            child: Padding(
          padding: const EdgeInsets.all(8.0),
          child: Stepper(
            steps: my_steps,
            type: StepperType.horizontal,
            controlsBuilder: (BuildContext context,
                {VoidCallback onStepContinue, VoidCallback onStepCancel}) {
              return Row(
                children: &lt;Widget&gt;[
                  Container(
                    child: null,
                  ),
                  Container(
                    child: null,
                  ),
                ],
              );
            },
            //type: StepperType.horizontal,
          ),
        ));
      },
    ),
  </code></pre>
  
  <p>After I uncomment the type I get this error:</p>
  
  <blockquote>
    <p>I/flutter (10148): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY
    ╞═════════════════════════════════════════════════════════ I/flutter
    (10148): The following assertion was thrown during performLayout():
    I/flutter (10148): RenderFlex children have non-zero flex but incoming
    height constraints are unbounded. I/flutter (10148): When a column is
    in a parent that does not provide a finite height constraint, for
    example if it is I/flutter (10148): in a vertical scrollable, it will
    try to shrink-wrap its children along the vertical axis. Setting a
    I/flutter (10148): flex on a child (e.g. using Expanded) indicates
    that the child is to expand to fill the remaining I/flutter (10148):
    space in the vertical direction.</p>
  </blockquote>