Fixed regex for sig file to replace only extension

[katiefaith]

Previously, relative paths would confuse the file name generation regex. With this change, only the final '.' character is matched as the beginning of the file extension.

[pelwell]

You could go one better and exclude /s from the match, so as not to truncate a path with a . if the filename has no extension (although it's unlikely to arise in practice).

[timg236]

Looks ok, not had chance to try this yet though

[katiefaith]

@pelwell good point. I updated the regex to [^./] to deal with that problem.

[pelwell]

Thanks!