Fix vet errors about formatting directives

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

integration-cli/docker_cli_build_test.go

@@ -3799,7 +3799,7 @@ func TestBuildStderr(t *testing.T) {
 		t.Fatal(err)
 	}
 	if stderr != "" {
-		t.Fatal("Stderr should have been empty, instead its: %q", stderr)
+		t.Fatalf("Stderr should have been empty, instead its: %q", stderr)
 	}
 	logDone("build - testing stderr")
 }