Fix #1196: extension adding methods error.

src/extensions/group-by/bootstrap-table-group-by.js

@@ -146,10 +146,7 @@
         originalData: undefined
     });
 
-    $.extend($.fn.bootstrapTable.methods, [
-        'collapseAll',
-        'expandAll'
-    ]);
+    $.fn.bootstrapTable.methods.push('collapseAll', 'expandAll');
 
     $.extend($.fn.bootstrapTable.COLUMN_DEFAULTS, {
         groupBySumGroup: false
@@ -228,4 +225,4 @@
             this.$el.treetable('expandNode', id);
         }
     }
-}(jQuery);
+}(jQuery);