added migrationId to migration

lib/migration.js

@@ -10,7 +10,8 @@ module.exports = (function() {
     this.migrator       = migrator
     this.path           = path
     this.filename       = Utils._.last(this.path.split('/'))
-    this.date           = Migration.stringToDate(split[split.length - 1])
+    this.migrationId    = parseInt(this.filename.match(/(.*)-.*/)[1])
+    this.date           = Migration.stringToDate(this.filename)
     this.queryInterface = this.migrator.queryInterface
     this.undoneMethods  = 0
   }