chore(package): update babel-plugin-syntax-flow to version 6.18.0 (#3664)

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -47,7 +47,7 @@
     "babel-cli": "6.24.0",
     "babel-core": "6.23.1",
     "babel-eslint": "^7.1.1",
-    "babel-plugin-syntax-flow": "6.13.0",
+    "babel-plugin-syntax-flow": "6.18.0",
     "babel-plugin-transform-flow-strip-types": "6.22.0",
     "babel-preset-es2015": "6.24.0",
     "babel-preset-stage-0": "6.22.0",