Update dependency sinon to v6 (#348)

Author: renovate[bot]

package-lock.json

@@ -50,7 +50,7 @@
     "portfinder": "1.0.13",
     "selenium-assistant": "5.3.0",
     "semver": "5.4.1",
-    "sinon": "5.0.7",
+    "sinon": "6.0.0",
     "which": "1.3.0"
   },
   "engines": {