cmd/checker: fix vet errors
diff --git a/cmd/checker/checker.go b/cmd/checker/checker.go
index 29892af..becca1b 100644
--- a/cmd/checker/checker.go
+++ b/cmd/checker/checker.go
@@ -143,7 +143,7 @@
 	for n, f := range ch.Files {
 		cfg := gerritfmt.Formatters[language]
 		if cfg == nil {
-			return nil, fmt.Errorf("language %q not configured")
+			return nil, fmt.Errorf("language %q not configured", language)
 		}
 		if !cfg.Regex.MatchString(n) {
 			continue
diff --git a/cmd/checker/main.go b/cmd/checker/main.go
index d455afe..1243562 100644
--- a/cmd/checker/main.go
+++ b/cmd/checker/main.go
@@ -47,7 +47,7 @@
 		// TODO: use inotify
 		for range time.Tick(time.Minute) {
 			if err := j.read(nm); err != nil {
-				log.Println("read %s: %v", nm, err)
+				log.Printf("read %s: %v", nm, err)
 			}
 		}
 	}()
@@ -118,7 +118,7 @@
 	if nm := *cookieJar; nm != "" {
 		g.Client.Jar, err = NewHardcodedJar(nm)
 		if err != nil {
-			log.Fatal("NewHardcodedJar: %v", err)
+			log.Fatalf("NewHardcodedJar: %v", err)
 		}
 	}
 	g.UserAgent = *agent