use bytes.Buffer, should work with older go versions

properties.go

@@ -8,6 +8,7 @@ package properties
 // BUG(frank): Write() does not allow to configure the newline character. Therefore, on Windows LF is used.
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"log"
@@ -766,7 +767,7 @@ func expand(s string, keys []string, prefix, postfix string, values map[string]s
 
 		for _, k := range keys {
 			if key == k {
-				var b strings.Builder
+				var b bytes.Buffer
 				b.WriteString("circular reference in:\n")
 				for _, k1 := range keys {
 					fmt.Fprintf(&b, "%s=%s\n", k1, values[k1])