fix border style without borderRadius

Summary:
closes #6721 closes #3159
before(without borderRadius)
![bug](https://cloud.githubusercontent.com/assets/1488195/14235087/fcf79f8a-f9eb-11e5-9d44-7ab1d131be24.jpg)

after
![fix](https://cloud.githubusercontent.com/assets/1488195/14235067/8cf128b4-f9eb-11e5-8170-ad3a146d6104.jpg)
Closes facebook/react-native#6789

Differential Revision: D3240657

Pulled By: mkonicek

fb-gh-sync-id: 4eb8f72d7278d880297fb73653ef530719af3d5b
fbshipit-source-id: 4eb8f72d7278d880297fb73653ef530719af3d5b

UIExplorer/ViewExample.js

@@ -46,7 +46,6 @@ var ViewBorderStyleExample = React.createClass({
         <View>
           <View style={{
             borderWidth: 1,
-            borderRadius: 5,
             borderStyle: this.state.showBorder ? 'dashed' : null,
             padding: 5
           }}>