Fix Select multiple select issue when has the same label

Author: e1emeb0t

package.json

@@ -1,6 +1,6 @@
 {
   "name": "element-react",
-  "version": "1.4.11",
+  "version": "1.4.12",
   "description": "Element UI for React",
   "private": false,
   "main": "dist/npm/es5/index.js",

src/select/Select.jsx

@@ -773,7 +773,7 @@ class Select extends Component {
       selected = selected.slice(0);
 
       selected.forEach((item, index) => {
-        if (item === option || item.currentLabel() === option.currentLabel()) {
+        if (item === option || item.props.value === option.props.value) {
           optionIndex = index;
         }
       });