fix Time component can't update when time prop updated.

https://segmentfault.com/q/1010000021110866
https://run.iviewui.com/GRzcErZn

examples/routers/time.vue

@@ -1,5 +1,7 @@
 <template>
     <div>
+        <Button @click="testUpdate()">Update Test</Button>
+        <br>
         <Time :time="time1" />
         <br>
         <Time :time="time2" />
@@ -10,6 +12,8 @@
     </div>
 </template>
 <script>
+    const baseTime = parseInt(Date.now() / 10000000) * 10000000
+
     export default {
         data () {
             return {
@@ -18,6 +22,12 @@
                 time3: (new Date()).getTime() - 1 * 1000,
                 time4: (new Date()).getTime() - 86400 * 60 * 1000,
             };
+        },
+
+        methods: {
+            testUpdate() {
+                this.time1 = parseInt(baseTime + Math.random() * 10000000)
+            }
         }
     };
 </script>

src/components/time/time.vue

@@ -49,6 +49,12 @@
                 ];
             }
         },
+        watch: {
+            time () {
+                // https://segmentfault.com/q/1010000021110866
+                if (!isServer) this.setTime()
+            }
+        },
         methods: {
             handleClick () {
                 if (this.hash !== '') window.location.hash = this.hash;
@@ -96,4 +102,4 @@
             if (this.timer) clearInterval(this.timer);
         }
     };
-</script>
+</script>