update .gitignore for pre-compiled android native libs that are used when not rebuilding native libs

.gitignore

@@ -70,4 +70,5 @@
 /jme3-ios/build/
 /jme3-android-native/openal-soft/
 /jme3-android-native/OpenALSoft.zip
-/jme3-android-native/stb_image/
+/jme3-android-native/stb_image/
+/jme3-android-native/libs/