Fix async.each in migration (loopbackio#262)

Author: DaGaMs

lib/migration.js

@@ -58,7 +58,7 @@ function mixinMigration(MySQL, mysql) {
 
     models = models || Object.keys(this._models);
 
-    async.each(models, function(model, done) {
+    async.eachSeries(models, function(model, done) {
       if (!(model in self._models)) {
         return process.nextTick(function() {
           done(new Error(g.f('Model not found: %s', model)));
@@ -136,7 +136,7 @@ function mixinMigration(MySQL, mysql) {
 
     models = models || Object.keys(this._models);
 
-    async.each(models, function(model, done) {
+    async.eachSeries(models, function(model, done) {
       self.getTableStatus(model, function(err, fields, indexes) {
         self.discoverForeignKeys(self.table(model), {}, function(err, foreignKeys) {
           if (err) console.log('Failed to discover "' + table + '" foreign keys', err);