chore(package): update sinon to version 6.0.1

Closes #74

Author: greenkeeper[bot]

package.json

@@ -65,7 +65,7 @@
     "nyc": "^11.0.1",
     "postcss": "^6.0.7",
     "postcss-modules": "^1.0.0",
-    "sinon": "^4.0.1",
+    "sinon": "^6.0.1",
     "sinon-chai": "^2.8.0",
     "string-hash": "^1.1.1"
   },