title: React Native Button Icon not showing
body: <p>I am using expo's snack, no icon ever showing correctly, what am I doing wrong?
  I test this snack <a href="https://snack.expo.io/?name=Button&amp;description=https%3A%2F%2Fcallstack.github.io%2Freact-native-paper%2Fbutton.html&amp;code=import%20*%20as%20React%20from%20%27react%27%3B%0Aimport%20%7B%20Button%20%7D%20from%20%27react-native-paper%27%3B%0A%0Aconst%20MyComponent%20%3D%20()%20%3D%3E%20(%0A%20%20%3CButton%20icon%3D%22camera%22%20mode%3D%22contained%22%20onPress%3D%7B()%20%3D%3E%20console.log(%27Pressed%27)%7D%3E%0A%20%20%20%20Press%20me%0A%20%20%3C%2FButton%3E%0A)%3B%0A%0Aexport%20default%20MyComponent%3B&amp;dependencies=react-native-paper" rel="nofollow noreferrer">https://callstack.github.io/react-native-paper/button.html</a>, and many other snack, but it always show rectangle icon. </p>
  
  <p><a href="https://i.stack.imgur.com/iSfep.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/iSfep.png" alt="Buttons always show rectangle icon"></a>
  I am using expo 36.0.0</p>