Merge pull request #8 from samgiles/master

Include Headers, Response and Request objects on the global scope on the server.

server.js

@@ -5,4 +5,7 @@ var noConflictSelf = global.self;
 global.self = {};
 require('whatwg-fetch');
 global.fetch = global.self.fetch;
+global.Headers = global.self.Headers;
+global.Request = global.self.Request;
+global.Response = global.self.Response;
 global.self = noConflictSelf;