fix: example/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-WEBPACKDEVSERVER-72405
- https://snyk.io/vuln/npm:braces:20180219
- https://snyk.io/vuln/npm:eslint:20180222

Author: snyk-bot

example/package.json

@@ -8,7 +8,7 @@
     "prop-types": "^15.6.2",
     "react": "^16.4.1",
     "react-dom": "^16.4.1",
-    "react-scripts": "^1.1.4",
+    "react-scripts": "^2.1.3",
     "react-syntax-highlighter": "^8.0.1",
     "react-editext": "link:.."
   },