fix SSH client leak bug

Author: Dreamacro

lib/ssh.js

@@ -6,7 +6,7 @@ module.exports = function(opt) {
   var agent = new http.Agent();
 
   agent.createConnection = function(options, fn) {
-    conn.on('ready', function() {
+    conn.once('ready', function() {
       conn.exec('docker system dial-stdio', function(err, stream) {
         if (err) {
           conn.end();
@@ -16,14 +16,14 @@ module.exports = function(opt) {
 
         fn(null, stream);
 
-        stream.on('close', () => {
+        stream.once('close', () => {
           conn.end();
           agent.destroy();
         });
       });
     }).connect(opt);
 
-    conn.on('end', () => agent.destroy());
+    conn.once('end', () => agent.destroy());
   };
 
   return agent;