fix(package): update query-string to version 6.12.1

Closes #66

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
     "path": "^0.12.7",
     "path-to-regexp": "^2.4.0",
     "prop-types": "^15.5.10",
-    "query-string": "^4.3.4",
+    "query-string": "^6.12.1",
     "url": "^0.11.0"
   },
   "devDependencies": {