title: native base drawer wont open with native-router-flux
body: <p>i have a problem with native-base and react-native-router-flux.
  The Drawer wont open when i click on the menu in the top bar (on snack you see just a questionmark instead of the menu icon) and i don't know whats wrong with the code.</p>
  
  <p>Could anyone help me with this or have a better example then the on on github?</p>
  
  <p>Code is on Snack:
  <a href="https://snack.expo.io/@snak3/test-with-native-base-drawer-and-native-router-flux" rel="nofollow noreferrer">https://snack.expo.io/@snak3/test-with-native-base-drawer-and-native-router-flux</a></p>