Update rules/rules.go

Use `strings.HasPrefix` to avoid panic on empty string.

Co-authored-by: Oleg Lobanov <oleg@lobanov.me>

rules/rules.go

@@ -22,7 +22,7 @@ type Rule struct {
 // MatchHidden matches paths with a basename
 // that begins with a dot.
 func MatchHidden(path string) bool {
-	return filepath.Base(path)[0] == '.'
+	return strings.HasPrefix(filepath.Base(path), ".")
 }
 
 // Matches matches a path against a rule.