Merge pull request kaisellgren#100 from close2/dev

documentation correction

README.md

@@ -64,8 +64,6 @@ Known headers (`list-unsubscribe`,...) should have their own subclass.
 See [gmail example](example/send_gmail.dart).
 
 ```dart
-import 'dart:io';
-
 import 'package:mailer/mailer.dart';
 import 'package:mailer/smtp_server.dart';
 
@@ -124,16 +122,16 @@ main() async {
  // Sending multiple messages with the same connection
  //
  // Create a smtp client that will persist the connection
- var client = SmtpPersistentClient(smtpServer);
+ var connection = PersistentConnection(smtpServer);
  
  // Send the first message
- await client.send(message);
+ await connection.send(message);
  
  // send the equivalent message
- await client.send(equivalentMessage);
+ await connection.send(equivalentMessage);
  
  // close the connection
- await client.close();
+ await connection.close();
  
 }
 ```