bug fixes: 'where' clause of false value not working.

Added "User-Agent" in headers.

Author: Aamod Pisat

package.json

@@ -1,14 +1,14 @@
 {
   "name": "contentstack",
-  "version": "3.1.0",
+  "version": "3.1.1",
   "description": "The Built.io Contentstack Javascript SDK",
   "homepage": "https://www.built.io/products/contentstack/overview",
   "author": {
     "name": "Built.io Contentstack",
     "url": "https://www.built.io/"
   },
   "main": "dist/node/contentstack.js",
-  "_id": "contentstack@3.0.0",
+  "_id": "contentstack@3.1.1",
   "scripts": {
     "test": "node test.js",
     "buildnode": "webpack --config webpack/webpack.node.js",