chore(package): update babel-plugin-syntax-flow to version 6.13.0 (#2457)

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -51,7 +51,7 @@
   "devDependencies": {
     "babel-cli": "6.11.4",
     "babel-core": "6.11.4",
-    "babel-plugin-syntax-flow": "6.8.0",
+    "babel-plugin-syntax-flow": "6.13.0",
     "babel-plugin-transform-flow-strip-types": "6.8.0",
     "babel-preset-es2015": "6.13.0",
     "babel-preset-stage-0": "6.5.0",