Update fsevents dependency version (facebook#6843)

Fixes facebook#6852.

I update the dependency version of fsevents because old versions was vulnerable (CWE-59). Vulnerability found with snyk.io report

Author: FrancoisRmn

packages/react-scripts/package.json

@@ -84,7 +84,7 @@
     "react-dom": "^16.8.4"
   },
   "optionalDependencies": {
-    "fsevents": "1.2.7"
+    "fsevents": "2.0.6"
   },
   "browserslist": {
     "production": [