Use browser-sync instead of docsify-cli to serve docs on local

[yhatt]

While editing document by yarn docs command, hot-reload in many pages by docsify-cli won't work because it does not support SPA.

Instead, we will use browser-sync to serve docsify on local with the hot reload support.

In addition, it reduce the dependency of remark in docisfy-cli with the version that has reported vulnerability. (It cannot remove resolution for remark because jsdoc is still using the old remark)