chore(package): update eslint-plugin-flowtype to version 3.1.0

Closes #73

Author: greenkeeper[bot]

package.json

@@ -80,7 +80,7 @@
     "eslint": "^4.19.0",
     "eslint-config-standard": "^11.0.0",
     "eslint-config-standard-react": "^6.0.0",
-    "eslint-plugin-flowtype": "^2.46.1",
+    "eslint-plugin-flowtype": "^3.1.0",
     "eslint-plugin-import": "^2.9.0",
     "eslint-plugin-node": "^6.0.1",
     "eslint-plugin-promise": "^3.7.0",