table: set width for each td>div.cell.el-tooltip element(#2198,#3128)

packages/table/src/table-column.js

@@ -290,7 +290,7 @@ export default {
       }
 
       return _self.showOverflowTooltip || _self.showTooltipWhenOverflow
-        ? <div class="cell el-tooltip">{ renderCell(h, data) }</div>
+        ? <div class="cell el-tooltip" style={'width:' + (data.column.realWidth || data.column.width) + 'px'}>{ renderCell(h, data) }</div>
         : <div class="cell">{ renderCell(h, data) }</div>;
     };
   },

packages/theme-default/src/table.css

@@ -40,6 +40,7 @@
 
     .el-tooltip.cell {
       white-space: nowrap;
+      min-width: 50px;
     }
 
     @e empty-block {