implemented initStepCountObserver method which allows listeners to be added to...

implemented initStepCountObserver method which allows listeners to be added to NativeAppEventEmitter for change:steps event

package.json

 {
   "name": "react-native-apple-healthkit",
-  "version": "0.1.2",
+  "version": "0.1.3",
   "description": "A React Native bridge module for interacting with Apple HealthKit data",
   "main": "index.js",
   "scripts": {