Update babel-plugin-transform-class-properties to v6.19.0

The `babel-plugin-transform-class-properties` v6.19.0 update will allow
us to remove the `babel-plugin-transform-es2015-destructuring` and
`babel-plugin-transform-es2015-parameters` as the class properties
transform will now work standalone and not require additional tranforms

Author: valscion

packages/babel-preset-react-app/package.json

@@ -11,7 +11,7 @@
     "index.js"
   ],
   "dependencies": {
-    "babel-plugin-transform-class-properties": "6.16.0",
+    "babel-plugin-transform-class-properties": "6.19.0",
     "babel-plugin-transform-es2015-destructuring": "6.16.0",
     "babel-plugin-transform-es2015-parameters": "6.17.0",
     "babel-plugin-transform-object-rest-spread": "6.16.0",