added shutdown to datefile

lib/appenders/dateFile.js

@@ -1,6 +1,7 @@
 "use strict";
 var streams = require('../streams')
 , layouts = require('../layouts')
+, async = require('async')
 , path = require('path')
 , os = require('os')
 , eol = os.EOL || '\n'
@@ -54,5 +55,18 @@ function configure(config, options) {
   return appender(config.filename, config.pattern, config.alwaysIncludePattern, layout);
 }
 
+function shutdown(cb) {
+  async.forEach(openFiles, function(file, done) {
+    if (!file.write(eol, "utf-8")) {
+      file.once('drain', function() {
+        file.end(done);
+      });
+    } else {
+      file.end(done);
+    }
+  }, cb);
+}
+
 exports.appender = appender;
 exports.configure = configure;
+exports.shutdown = shutdown;