bump NDK APP_PLATFORM to android-16 (facebook#19830)

Summary:
This PR will bump NDK APP_PLATFORM to android-16. Below is the excerpt from NDK documentation

> This variable contains the minimum Android platform version you want to support. For example, a value of android-15 specifies that your library uses APIs that are not available below Android 4.0.3 (API level 15) and can't be used on devices running a lower platform version. For a complete list of platform names and corresponding Android system images, see Android NDK Native APIs.
Closes facebook#19830

Differential Revision: D8620017

Pulled By: hramos

fbshipit-source-id: 0b5578f130938e3ddae03fb855784193183243cf

Author: dulmandakh

ReactAndroid/src/main/jni/Application.mk

@@ -1,7 +1,7 @@
 APP_BUILD_SCRIPT := Android.mk
 
 APP_ABI := armeabi-v7a x86
-APP_PLATFORM := android-9
+APP_PLATFORM := android-16
 
 APP_MK_DIR := $(dir $(lastword $(MAKEFILE_LIST)))