title: How can I change the height of the tabs in MaterialTopTabNavigator?
body: <p>Currently the tabs are set at a fixed size, leaving a lot of white space above them.</p>
  <p>I'd like to be able to adjust the height of the tabs.</p>
  <p>The only height setting I can find in the source code is for the size of the icon.</p>
  <p>How can I change the height of the tabs?</p>