update eslint-plugin-react to 7.21.5 version

Summary:
The current available version of eslint-plugin-react is 7.21.4.
Update it to 7.21.5 to be able to use function-component-definition rule https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/function-component-definition.md

Changelog: [Internal]

Reviewed By: cpojer

Differential Revision: D24619420

fbshipit-source-id: 3097c4d920aa41b2dcced8d0ef5224b04a36effe

repo-config/package.json

@@ -29,7 +29,7 @@
     "eslint-plugin-jest": "22.4.1",
     "eslint-plugin-jsx-a11y": "6.2.1",
     "eslint-plugin-prettier": "2.6.2",
-    "eslint-plugin-react": "7.12.4",
+    "eslint-plugin-react": "7.21.5",
     "eslint-plugin-react-hooks": "^4.0.7",
     "eslint-plugin-react-native": "3.8.1",
     "eslint-plugin-relay": "1.7.1",