Update clone method to include indexes

Author: clozanosanchez

lib/schema.js

@@ -274,6 +274,7 @@ Schema.prototype.clone = function() {
   s.methods = utils.clone(this.methods);
   s.statics = utils.clone(this.statics);
   s._plugins = utils.clone(this._plugins);
+  s._indexes = utils.clone(this._indexes);
   s.s.hooks = this.s.hooks.clone();
   return s;
 };