fix undefined of proxy or exclude

Author: WhatAKitty

package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-fetch-mock",
-  "version": "0.5.2",
+  "version": "0.5.3",
   "description": "fetch mock for reactjs",
   "main": "index.js",
   "scripts": {

src/index.js

@@ -14,8 +14,8 @@ class FetchMock {
 
     this.urls = [];
     this.raw = options.fetch;
-    this.exclude = options.exclude;
-    this.proxy = options.proxy;
+    this.exclude = options.exclude || [];
+    this.proxy = options.proxy || [];
 
     this.loadMocks = this.loadMocks.bind(this);
     this.loadMock = this.loadMock.bind(this);