chore(package): update proxyquire to version 2.1.3

Closes #24

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
   },
   "devDependencies": {
     "mocha": "^5.0.0",
-    "proxyquire": "^1.7.11",
+    "proxyquire": "^2.1.3",
     "sinon": "^5.0.0",
     "standard": "^10.0.1",
     "semantic-release": "^7.0.1"