[Bug Report] tab disabled-color 失效bug

### VUX version
2.9.2

### OS/Browsers version
chrome

### Vue version
2.6.9

### Code

```html

{{item.text}}

listTab: [
{ text: "选择省", disabled: false },
{ text: "选择市", disabled: false },
{ text: "选择区/县", disabled: false },
{ text: "选择乡镇", disabled: false }
],

this.listTab[2].disabled = true;

```

### Steps to reproduce
动态改变tab-item disabled 状态为true 时 disabled-color 失效，具体表现为

禁用样式被默认样式覆盖

### What is Expected?
改变tab-item disabled 时字体样式动态变更为设置的字体样式

### What is actually happening?
改变tab-item disabled 时字体样式被默认样式覆盖