Update to sinon@7

Author: jwilsson

package.json

@@ -38,7 +38,7 @@
     "eslint": "^5.0.0",
     "eslint-config-lesshint": "^1.0.3",
     "mocha": "^5.0.0",
-    "sinon": "^6.0.0",
+    "sinon": "^7.2.2",
     "vinyl": "^2.1.0"
   },
   "license": "MIT",