Update regular expression to include all allowed characters.

This is as per the "Debian Policy Manual, Chapter 5 - Control files and their fields", see:

  https://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version

Fixes #2417.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>