fix: upgrade eslint-plugin-flowtype from 2.35.0 to 2.50.3

Snyk has created this PR to upgrade eslint-plugin-flowtype from 2.35.0 to 2.50.3.

See this package in NPM:
https://www.npmjs.com/package/eslint-plugin-flowtype

See this project in Snyk:
https://app.snyk.io/org/davidkindler/project/6865432e-9ae7-40aa-ab6d-807d59d4dccc?utm_source=github&utm_medium=upgrade-pr

package.json

@@ -20,7 +20,7 @@
     "eslint": "4.18.2",
     "eslint-config-react-app": "^2.0.0",
     "eslint-loader": "1.9.0",
-    "eslint-plugin-flowtype": "2.35.0",
+    "eslint-plugin-flowtype": "2.50.3",
     "eslint-plugin-import": "2.7.0",
     "eslint-plugin-jsx-a11y": "5.1.1",
     "eslint-plugin-react": "7.1.0",