asynqmon: Not working on Windows

Hi, great project. I’m trying using it on Windows, but can’t get it to work.

When running and trying to access the browser, the following error is displayed: open ui\build\index.html: file does not exist

I have done some diging and have found the problem, but don’t know the right “fix”, so for this reason I’m opening this issue instead of PR.

Basically on this line, filepath.Abs returns C:\ https://github.com/hibiken/asynqmon/blob/0eb9d88c5365d7f34c1a9ff61518a5075170bb41/main.go#L59

This causes problems with the check if is / https://github.com/hibiken/asynqmon/blob/0eb9d88c5365d7f34c1a9ff61518a5075170bb41/main.go#L65 There is a problem with filepath.Join as well, since it will use \ and GO embed.FS will not find the file then. https://golang.org/pkg/embed/#hdr-Directives

The path separator is a forward slash, even on Windows systems.

The only way I could get it to work was making the following changes:

p := r.URL.Path
if filepath.IsAbs(p) {
	p = srv.indexFilePath()
} else {
	p = path.Join(srv.staticDirPath, p)
}

// ...
func (srv *staticFileServer) indexFilePath() string {
	return path.Join(srv.staticDirPath, srv.indexFileName)
}