Fix typo...
diff --git a/format_checkers.go b/format_checkers.go
index 11845fa..5e2f304 100644
--- a/format_checkers.go
+++ b/format_checkers.go
@@ -169,7 +169,7 @@
 }
 
 func (f HostnameFormatChecker) IsFormat(input string) bool {
-	return rxHostname.MatchString(input) && len(string) < 256
+	return rxHostname.MatchString(input) && len(input) < 256
 }
 
 func (f UUIDFormatChecker) IsFormat(input string) bool {