[npm] added es script for running elasticsearch with esvm

CONTRIBUTING.md

@@ -35,10 +35,10 @@ Please make sure you have signed the [Contributor License Agreement](http://www.
   npm install
   ```
 
-- Start elasticsearch, you can use [esvm](https://github.com/simianhacker/esvm) to make that easier.
+- Start elasticsearch
 
   ```sh
-  grunt esvm:dev:keepalive
+  npm run es
   ```
 
 - Start the development server.

package.json

@@ -42,7 +42,8 @@
     "build": "grunt build",
     "start": "./bin/kibana --dev",
     "precommit": "grunt lintStagedFiles",
-    "karma": "karma start"
+    "karma": "karma start",
+    "es": "grunt esvm:dev:keepalive"
   },
   "repository": {
     "type": "git",