Use primaryKeyField in Model#count

fixes #3712

lib/model.js

@@ -856,7 +856,7 @@ module.exports = (function() {
 
 
     var col = '*';
     var col = '*';
     if (options.include) {
     if (options.include) {
-      col = this.name + '.' + this.primaryKeyAttribute;
+      col = this.name + '.' + this.primaryKeyField;
       expandIncludeAll.call(this, options);
       expandIncludeAll.call(this, options);
       validateIncludedElements.call(this, options);
       validateIncludedElements.call(this, options);
     }
     }