Update README.md

Fix "Operand of postfix '!' should have optional type" by removing extraneous `!` after `URL`

README.md

@@ -687,7 +687,7 @@ enum Router: URLRequestConvertible {
 
     var URLRequest: NSURLRequest {
         let URL = NSURL(string: Router.baseURLString)!
-        let mutableURLRequest = NSMutableURLRequest(URL: URL!.URLByAppendingPathComponent(path))
+        let mutableURLRequest = NSMutableURLRequest(URL: URL.URLByAppendingPathComponent(path))
         mutableURLRequest.HTTPMethod = method.rawValue
 
         if let token = Router.OAuthToken {