同步 UI Kit 报错
#### Please tell us your OS and Sketch version when create issues.

- [x] WeSketch-1.4.2
- [x] OS Version: `macOS (10.13.4)`
- [x] Sketch Version: `v49.3`

#### Issues below
同步 UI Kit 后报错
![image](https://user-images.githubusercontent.com/902283/39536610-ae4fd210-4e69-11e8-851e-54bf15136604.png)
![image](https://user-images.githubusercontent.com/902283/39536631-bc9f7546-4e69-11e8-859b-82a4b47d54ac.png)

