fix drawer: next Tick computed scroll height

Author: AmyFoxFN

example/pages/drawer/custom.vue

@@ -81,6 +81,4 @@
     .cube-drawer-item_active
       color: #fc9153
       background-color: transparent
-    .cube-drawer-panel
-      overflow: hidden
 </style>

example/pages/drawer/default.vue

@@ -69,6 +69,4 @@
     left: 0
     bottom: 0
     width: 100%
-    .cube-drawer-panel
-      overflow: hidden
 </style>

src/components/drawer/drawer-panel.vue

@@ -46,7 +46,9 @@
         this.scrollToTop()
       },
       isVisible() {
-        this.refresh()
+        this.$nextTick(() => {
+          this.refresh()
+        })
       }
     },
     mounted() {
@@ -84,6 +86,7 @@
     height: 100%
     flex: 1
     width: 170px
+    overflow: hidden
     background-color: $drawer-panel-bgc
     box-shadow: 0 1px 2px rgba(0, 0, 0, .2)
     + .cube-drawer-panel