fixed in multiple type, wrong position of popper

fixed in multiple type, when select some options, the position of popper not recalculation, so the position is wrong. By the way, it resolve the problem: when select one option, scroll page, throw many errors of popper.

src/components/select/select.vue

@@ -549,6 +549,7 @@
                     const inputField = this.$el.querySelector('input[type="text"]');
                     if (!this.autoComplete) this.$nextTick(() => inputField.focus());
                 }
+                this.broadcast('Drop', 'on-update-popper');
             },
             onQueryChange(query) {
                 this.query = query;