Fixed a bug that wrong sql generated when deleting object that has a specific fi…

…eld as a primary key in postgres.

lib/dialects/postgres/query-generator.js

@@ -395,7 +395,9 @@ var QueryGenerator = {
     primaryKeys[tableName] = primaryKeys[tableName] || [];
 
     if (!!model && primaryKeys[tableName].length < 1) {
-      primaryKeys[tableName] = Object.keys(model.primaryKeys);
+      primaryKeys[tableName] = Utils._.map(Object.keys(model.primaryKeys), function(k){
+        return model.primaryKeys[k].field;
+      });
     }
 
     if (options.limit) {