fix(table): TableHeader get wrong width, when column width props is String type

keep same type(String/Number) with Table width props

src/components/table/table.vue

@@ -834,6 +834,7 @@
                 columns.forEach((column, index) => {
                     column._index = index;
                     column._columnKey = columnKey++;
+                    column.width = parseInt(column.width);
                     column._width = column.width ? column.width : '';    // update in handleResize()
                     column._sortType = 'normal';
                     column._filterVisible = false;