Add missing bind methods for gesture responder.

Somehow the context is getting dropped *some of the time*, so that
`this` becomes undefined inside `onResponderGrant`. Binding the
methods to the instance fixes the issue.

It's unclear how it's only happening some of the time -- usually
binding issues will become immediate apparent with React -- so my
best guess is there's some detail inside the React Native system
where the context can be dropped.

src/libraries/ViewTransformer/index.js

@@ -100,10 +100,10 @@ export default class ViewTransformer extends React.Component {
             onStartShouldSetResponder: (evt, gestureState) => true,
             onMoveShouldSetResponderCapture: (evt, gestureState) => true,
             // onMoveShouldSetResponder: this.handleMove,
-            onResponderMove: this.onResponderMove,
-            onResponderGrant: this.onResponderGrant,
-            onResponderRelease: this.onResponderRelease,
-            onResponderTerminate: this.onResponderRelease,
+            onResponderMove: this.onResponderMove.bind(this),
+            onResponderGrant: this.onResponderGrant.bind(this),
+            onResponderRelease: this.onResponderRelease.bind(this),
+            onResponderTerminate: this.onResponderRelease.bind(this),
             onResponderTerminationRequest: (evt, gestureState) => false, // Do not allow parent view to intercept gesture
             onResponderSingleTapConfirmed: (evt, gestureState) => {
                 this.props.onSingleTapConfirmed && this.props.onSingleTapConfirmed();