Update eslint-plugin-flowtype to the latest version 🚀 (#870)

* chore(package): update eslint-plugin-flowtype to version 3.12.1

* chore(package): update lockfile package-lock.json

Author: greenkeeper[bot]

package-lock.json

@@ -53,7 +53,7 @@
     "codecov": "3.5.0",
     "cross-env": "5.2.0",
     "eslint": "6.0.1",
-    "eslint-plugin-flowtype": "3.12.0",
+    "eslint-plugin-flowtype": "3.12.1",
     "express": "4.17.1",
     "gulp": "4.0.2",
     "gulp-babel": "8.0.0",