[fix] BackHandler export; remove BackAndroid

Fix #673

src/apis/BackHandler/index.js

@@ -12,7 +12,7 @@
 
 function emptyFunction() {}
 
-const BackAndroid = {
+const BackHandler = {
   exitApp: emptyFunction,
   addEventListener() {
     return {
@@ -22,4 +22,4 @@ const BackAndroid = {
   removeEventListener: emptyFunction
 };
 
-export default BackAndroid;
+export default BackHandler;

src/module.js

@@ -9,7 +9,7 @@ import Animated from './apis/Animated';
 import AppRegistry from './apis/AppRegistry';
 import AppState from './apis/AppState';
 import AsyncStorage from './apis/AsyncStorage';
-import BackAndroid from './apis/BackAndroid';
+import BackHandler from './apis/BackHandler';
 import Clipboard from './apis/Clipboard';
 import Dimensions from './apis/Dimensions';
 import Easing from './apis/Easing';
@@ -73,7 +73,7 @@ export {
   AppRegistry,
   AppState,
   AsyncStorage,
-  BackAndroid,
+  BackHandler,
   Clipboard,
   Dimensions,
   Easing,
@@ -138,8 +138,7 @@ const ReactNative = {
   AppRegistry,
   AppState,
   AsyncStorage,
-  BackAndroid,
-  BackHandler: BackAndroid,
+  BackHandler,
   Clipboard,
   Dimensions,
   Easing,