fix file mode,it should be octal expressed

Signed-off-by: Guangming Wang <guangming.wang@daocloud.io>

pkg/repo/repo_test.go

@@ -241,7 +241,7 @@ func TestWriteFile(t *testing.T) {
 		t.Errorf("failed to create test-file (%v)", err)
 	}
 	defer os.Remove(repoFile.Name())
-	if err := sampleRepository.WriteFile(repoFile.Name(), 744); err != nil {
+	if err := sampleRepository.WriteFile(repoFile.Name(), 0744); err != nil {
 		t.Errorf("failed to write file (%v)", err)
 	}