remove unnecessary judgment & add vue dependency

Author: lishengzxc

package.json

@@ -42,6 +42,7 @@
     "webpack-dev-server": "^1.14.0"
   },
   "dependencies": {
+    "vue": "^1.0.25",
     "vue-popup": "^0.1.8"
   }
-}
+}

src/msgbox.vue

@@ -263,11 +263,9 @@
 
       visible(val) {
         if (val && this.$type === 'prompt') {
-          setTimeout(() => {
-            if (this.$els.input) {
-              this.$els.input.focus();
-            }
-          }, 500);
+          Vue.nextTick(() => {
+            this.$els.input.focus();
+          });
         }
       }
     },