API: cosmetic fix for timestamp comment

Hi Bradley,

I have a small code change: the API attribute filter generator was emitting the timestamp comment with no space before the closing comment tag.  That got our tools confused, did not identify the line as a timestamp comment and each time thought the contents had changed.

I think it's good practice to have a space before closing the comment, so I'm changing this here instead in our signing tools - thanks in advance for merging this.

Cheers,
Vlad