fix go vet

serialize.go:361: unreachable code
serialize.go:415: arg o for printf verb %s of wrong type: int
serialize.go:422: arg o for printf verb %s of wrong type: int
worker.go:354: unreachable code
ninja_test.go:134: missing argument for Errorf("%q"): format reads arg 2, have only 1 args
rule_parser_test.go:160: arg *got for printf verb %q of wrong type: main.Rule
diff --git a/rule_parser_test.go b/rule_parser_test.go
index 17ed418..d2dcf19 100644
--- a/rule_parser_test.go
+++ b/rule_parser_test.go
@@ -157,7 +157,7 @@
 			continue
 		}
 		if !reflect.DeepEqual(*got, tc.want) {
-			t.Errorf(`r.parse(%q); r=%q, want %q`, tc.in, *got, tc.want)
+			t.Errorf(`r.parse(%q); r=%#v, want %#v`, tc.in, *got, tc.want)
 		}
 		if tc.assign != nil {
 			if assign == nil {