chore(package): update fetch-mock to version 5.12.0

Closes #87

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "codecov": "2.2.0",
     "dateformat": "2.0.0",
     "execa": "0.7.0",
-    "fetch-mock": "5.11.0",
+    "fetch-mock": "5.12.0",
     "http-server": "0.10.0",
     "istanbul-instrumenter-loader": "2.0.0",
     "karma": "1.7.0",