修复：popup的zIndex转换为number (#24)

src/mixins/popup/index.js

@@ -66,15 +66,14 @@ export default {
     /**
      * 显示popup
      */
-    open(options) {
+    open() {
       if (this.opened) return;
 
       this.opening = true;
 
       this.$emit('input', true);
 
-      const props = merge({}, this, options);
-      const zIndex = props.zIndex;
+      const zIndex = this.zIndex;
 
       // 如果属性中传入了`zIndex`，则覆盖`popupContext`中对应的`zIndex`
       if (zIndex) {

src/mixins/popup/popup-context.js

@@ -25,7 +25,7 @@ const PopupContext = {
   },
 
   plusKeyByOne(key) {
-    const oldVal = context[key];
+    const oldVal = +context[key];
     context[key] = oldVal + 1;
 
     return oldVal;