Custom Blocks page is not found on documentation

### Version
15.0.0

### Reproduction link
[https://vue-loader.vuejs.org/custom-blocks.html](https://vue-loader.vuejs.org/custom-blocks.html)

### Steps to reproduce
SFC spec link error
https://vue-loader.vuejs.org/spec.html
Custom Blocks can not open

### What is expected?
should open

### What is actually happening?
can not open