Fix tarball file path to remove the output prefix…

This would create weirdly invalid
tarball (`{output}/tasks/{task-name}` instead of `tasks/{task-name}`)
when release with `--output` not being the current directory.

Signed-off-by: Vincent Demeester <[email protected]>

internal/cmd/release.go

@@ -200,7 +200,7 @@ func addToArchive(tw *tar.Writer, filename, output string) error {
 	// If we don't do this the directory strucuture would
 	// not be preserved
 	// https://golang.org/src/archive/tar/common.go?#L626
-	header.Name = strings.TrimPrefix(filename, filepath.Base(output)+"/")
+	header.Name = strings.TrimPrefix(filename, filepath.Join(output, "/")+"/")
 
 	// Write file header to the tar archive
 	err = tw.WriteHeader(header)