fix(reduce): do not set $data._value in updateValue if reduce option is set

Closes #1210

src/components/Select.vue

@@ -713,7 +713,7 @@
        * @param value
        */
       updateValue (value) {
-        if (this.isTrackingValues) {
+        if (typeof this.value === 'undefined') {
           // Vue select has to manage value
           this.$data._value = value;
         }
@@ -989,7 +989,6 @@
        */
       selectedValue () {
         let value = this.value;
-
         if (this.isTrackingValues) {
           // Vue select has to manage value internally
           value = this.$data._value;