chore(package): update prop-types to version 15.6.1

Author: greenkeeper[bot]

package.json

@@ -56,7 +56,7 @@
     "diff": "3.4.0",
     "execa": "0.9.0",
     "nyc": "11.4.1",
-    "prop-types": "15.6.0",
+    "prop-types": "15.6.1",
     "react": "^16.0.0",
     "rimraf": "2.6.2",
     "source-map-support": "0.5.3",