buffer_test, transport_test: fix 'go vet' issues
diff --git a/transport_test.go b/transport_test.go
index 0622923..d752da1 100644
--- a/transport_test.go
+++ b/transport_test.go
@@ -76,11 +76,11 @@
 		t.Errorf("Response.Request = %p; want %p", res.Request, req)
 	}
 	if res.TLS == nil {
-		t.Errorf("Response.TLS = nil; want non-nil", res.TLS)
+		t.Error("Response.TLS = nil; want non-nil")
 	}
 	slurp, err := ioutil.ReadAll(res.Body)
 	if err != nil {
-		t.Error("Body read: %v", err)
+		t.Errorf("Body read: %v", err)
 	} else if string(slurp) != body {
 		t.Errorf("Body = %q; want %q", slurp, body)
 	}