Select: fix single mode allow-create not working in Vue 2.2.x (#3984)

packages/select/src/select.vue

@@ -103,7 +103,6 @@
   import { addClass, removeClass, hasClass } from 'element-ui/src/utils/dom';
   import { addResizeListener, removeResizeListener } from 'element-ui/src/utils/resize-event';
   import { t } from 'element-ui/src/locale';
-  import merge from 'element-ui/src/utils/merge';
   const sizeMap = {
     'large': 42,
     'small': 30,
@@ -197,7 +196,7 @@
       return {
         options: [],
         cachedOptions: [],
-        createdOption: null,
+        createdLabel: null,
         createdSelected: false,
         selected: this.multiple ? [] : {},
         isSelect: true,
@@ -289,7 +288,7 @@
             if (this.selected) {
               if (this.filterable && this.allowCreate &&
                 this.createdSelected && this.createdOption) {
-                this.selectedLabel = this.createdOption.currentLabel;
+                this.selectedLabel = this.createdLabel;
               } else {
                 this.selectedLabel = this.selected.currentLabel;
               }
@@ -396,7 +395,7 @@
         if (!this.multiple) {
           let option = this.getOption(this.value);
           if (option.created) {
-            this.createdOption = merge({}, option);
+            this.createdLabel = option.currentLabel;
             this.createdSelected = true;
           } else {
             this.createdSelected = false;