Merge pull request #92 from pietropizzi/master

ViewShot is the default export so update the docs

README.md

 ## Recommended High Level API
 
 ```js
-import { ViewShot } from "react-native-view-shot";
+import ViewShot from "react-native-view-shot";
 
 class ExampleCaptureOnMountManually extends Component {
   componentDidMount () {