upgrade example's RN

Author: gre

example/package.json

@@ -15,7 +15,7 @@
     "bunny": "^1.0.1",
     "gl-mat4": "^1.1.4",
     "react": "16.0.0-alpha.12",
-    "react-native": "^0.48.2",
+    "react-native": "^0.49.3",
     "react-native-webgl": "file:..",
     "react-navigation": "1.0.0-beta.12",
     "regl": "^1.3.0",