chore(package): update sinon to version 7.3.0

Closes #67

Author: greenkeeper[bot]

package.json

@@ -31,7 +31,7 @@
     "karma-sinon": "^1.0.5",
     "mocha": "^3.1.0",
     "power-assert": "^1.4.4",
-    "sinon": "^4.0.0"
+    "sinon": "^7.3.0"
   },
   "files": [
     "README.md",