Update react monorepo to v16.12.0 (#956)

Author: renovate[bot]

src/React.Core/package-lock.json

@@ -9,8 +9,8 @@
     "@babel/core": "7.6.4",
     "@babel/standalone": "7.7.4",
     "prop-types": "15.7.2",
-    "react": "16.10.2",
-    "react-dom": "16.10.2",
+    "react": "16.12.0",
+    "react-dom": "16.12.0",
     "webpack": "4.41.2",
     "webpack-cli": "3.3.10"
   }