chore(package): update sinon to version 9.0.1

Closes #51

Author: greenkeeper[bot]

package.json

@@ -63,7 +63,7 @@
     "mocha": "^5.2.0",
     "poll-forever": "^1.0.0",
     "request": "^2.87.0",
-    "sinon": "^6.1.3",
+    "sinon": "^9.0.1",
     "sinon-chai": "^3.2.0",
     "traverson-mock-response": "1.1.0",
     "traverson-test-server": "1.12.1"