[PR #1633] Fixed sample code in the README where error was used incorrectly.

README.md

@@ -240,7 +240,7 @@ The `response` handler does NOT evaluate any of the response data. It merely for
 Alamofire.request("https://httpbin.org/get").response { response in
     print("Request: \(response.request)")
     print("Response: \(response.response)")
-    print("Error: \(response.data)")
+    print("Error: \(response.error)")
 
     if let data = response.data, let utf8Text = String(data: data, encoding: .utf8) {
     	print("Data: \(utf8Text)")