Merge pull request #18 from matthew-andrews/dont-force-fetch

Don't redefine global fetch.

server.js

@@ -1,9 +1,13 @@
 "use strict";
 
 var realFetch = require('node-fetch');
-module.exports = global.fetch = function(url, options) {
+module.exports = function(url, options) {
 	if (/^\/\//.test(url)) {
 		url = 'https:' + url;
 	}
 	return realFetch.call(this, url, options);
 };
+
+if (!global.fetch) {
+	global.fetch = module.exports;
+}