cmd/gitmirror: add missing len(refHash) parameter to log.Printf call

This change fixes an incorrect number of parameters provided to
a log.Printf call. It's caught by vet and causes go test to fail.

Change-Id: Ic06a2d571959cf2a93b53e7765b675ed67ec7830
Reviewed-on: https://go-review.googlesource.com/c/156343
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/cmd/gitmirror/gitmirror.go b/cmd/gitmirror/gitmirror.go
index f9d75af..b41299d 100644
--- a/cmd/gitmirror/gitmirror.go
+++ b/cmd/gitmirror/gitmirror.go
@@ -1535,7 +1535,7 @@
 		f := strings.Fields(bs.Text())
 		if len(f) < 2 {
 			log.Printf("WARNING: skipping bogus ref line %d, %q (report this to https://golang.org/issue/29560)", line, bs.Text())
-			log.Printf("         refHash so far: %d entries, %s\n", condTrunc(fmt.Sprintf("%q", refHash), 500))
+			log.Printf("         refHash so far: %d entries, %s\n", len(refHash), condTrunc(fmt.Sprintf("%q", refHash), 500))
 			continue
 		}
 		refHash[f[1]] = f[0]