Update sinon requirement from ~1.7.3 to ~2.4.1

Updates the requirements on [sinon](https://github.com/sinonjs/sinon) to permit the latest version.
- [Release notes](https://github.com/sinonjs/sinon/releases)
- [Changelog](https://github.com/sinonjs/sinon/blob/master/CHANGELOG.md)
- [Commits](sinonjs/sinon@v1.7.3...v2.4.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -25,7 +25,7 @@
   "devDependencies": {
     "mocha": "~5.2.0",
     "nock": "~10.0.6",
-    "sinon": "~1.7.3"
+    "sinon": "~2.4.1"
   },
   "engines": {
     "node": ">=0.10.x",