Loading Mermaid plugin is slow

Add Mermaid and the plugin:
```
<script src="//unpkg.com/mermaid/dist/mermaid.js"></script>
<script src="//unpkg.com/docsify-mermaid@latest/dist/docsify-mermaid.js"></script>
<script>mermaid.initialize({ startOnLoad: true });</script>
```

mermaid.js  file is large，3.36MB

Just a few The mermaid is used in the MD file. Please find the optimization method. Thank you




