Add '--no-single-branch' to shallow clone

Shallow clone should still download all branches and tags to make sure
we can find proper version.

This fixes regression introduced by 1dc2b53 as previously after shallow
clone we still run fetch on newly cloned repo which updated branches and
tags.

newt/downloader/downloader.go

@@ -947,7 +947,7 @@ func (gd *GithubDownloader) Clone(commit string, dstPath string) error {
 	}
 
 	if util.ShallowCloneDepth > 0 {
-		cmd = append(cmd, "--depth", strconv.Itoa(util.ShallowCloneDepth))
+		cmd = append(cmd, "--depth", strconv.Itoa(util.ShallowCloneDepth), "--no-single-branch")
 	}
 
 	cmd = append(cmd, url, dstPath)