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

Closes #23

Author: greenkeeper[bot]

package.json

@@ -51,7 +51,7 @@
   },
   "devDependencies": {
     "eslint-config-xo-react": "0.16.0",
-    "eslint-plugin-flowtype": "2.46.3",
+    "eslint-plugin-flowtype": "3.1.0",
     "eslint-plugin-react": "7.8.0",
     "jest": "22.4.3",
     "xo": "0.21.0"