Date wrong in generated pr commit message

[imnasnainaec]

In the pr generated by #1439, the commit message doesn't display the "Updated:" date as intended. E.g.:

Here's the line of code that needs to be fixed: https://github.com/sillsdev/libpalaso/pull/1439/files#diff-f02fb6b466bcfbe7ca0799cffc0df614bbe92d35f1cec966603b08c8af6c4cc4R235