chore(package): update sinon to version 7.2.5

Closes #73

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "jshint": "^2.9.5",
     "mocha": "~5.2.0",
     "nock": "~10.0.0",
-    "sinon": "~6.0.1",
+    "sinon": "~7.2.5",
     "testen": "^2.2.1"
   },
   "dependencies": {