title: Cannot set padding to 0 on Material UI Button
body: <p>I'm using a normal <code>Button</code> from <code>Material-UI</code> for <code>React</code> tried adding the following style</p>
  
  <pre><code>button: {
      display: 'inline-block',
      padding:0
    }
  </code></pre>
  
  <p>to this button</p>
  
  <pre><code>&lt;Button className={classes.button}&gt; I'm a Test Button &lt;/Button&gt;
  </code></pre>
  
  <p>What I obtain is that the padding for the <strong>right/left</strong> side is correctly set to 0, while the one for <strong>top/bottom</strong> is not updated, see the attached image. <br></p>
  
  <p>Is this a bug? Or what's the correct way to achieve this?</p>
  
  <p><em>EDIT:</em>
  Material-UI version: <strong><em>v1.0.0-beta.20</em></strong></p>
  
  <p><a href="https://i.stack.imgur.com/EEQmY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/EEQmY.png" alt="enter image description here"></a></p>