inputNumber组件添加placeholder属性

src/components/input-number/input-number.vue

@@ -30,7 +30,8 @@
                 @change="change"
                 :readonly="readonly || !editable"
                 :name="name"
-                :value="formatterValue">
+                :value="formatterValue"
+                :placeholder="placeholder">
         </div>
     </div>
 </template>
@@ -120,7 +121,11 @@
             },
             parser: {
                 type: Function
-            }
+            },
+            placeholder: {
+                type: String,
+                default: ''
+            },
         },
         data () {
             return {