Add prepare script to run build step when installing from git

Author: ianyong

package.json

@@ -25,7 +25,8 @@
     "test:coverage": "nyc npm run test:unit",
     "refresh": "rm -rf ./node_modules ./package-lock.json && npm install",
     "precommit": "npm run lint && npm run format:test",
-    "prepush": "npm run lint && npm run test"
+    "prepush": "npm run lint && npm run test",
+    "prepare": "npm run build"
   },
   "author": "AWS Lambda",
   "license": "Apache-2.0",