Upgrade gas-client (#164)

Uses latest UMD build for gas-client and externalizes the package to further reduce client bundle size

package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-google-apps-script",
-  "version": "2.1.0",
+  "version": "2.1.1",
   "description": "Starter project for using React with Google Apps Script",
   "repository": {
     "type": "git",
@@ -85,7 +85,7 @@
     "eslint-plugin-promise": "^6.0.0",
     "eslint-plugin-react": "^7.30.0",
     "eslint-plugin-standard": "^5.0.0",
-    "gas-client": "^1.0.0",
+    "gas-client": "^1.1.1",
     "gas-lib": "^2.0.4",
     "gas-types-detailed": "^1.1.0",
     "gas-webpack-plugin": "^2.2.2",