Potential fix for #1057

Tests for the undo flag would definitely be a good idea, too.

bin/sequelize

@@ -113,7 +113,7 @@ if(typeof program.env === 'string') {
   configuration.environment = program.env
 }
 
-if (program.migrate) {
+if (program.migrate || program.undo) {
   if (configFileExists()) {
     var config
       , options  = {}