chore(package): update proxyquire to version 2.1.2

Closes #50

Author: greenkeeper[bot]

package.json

@@ -31,7 +31,7 @@
     "eslint-config-pedant": "^1.0.0",
     "mocha": "^5.0.0",
     "nyc": "^11.3.0",
-    "proxyquire": "^1.8.0",
+    "proxyquire": "^2.1.2",
     "sinon": "^4.1.2",
     "sinon-chai": "^2.14.0"
   },