security/vuxml: Fix invalid escape sequence in Python re

ports/security/vuxml/files/extra-validation.py:13:

SyntaxWarning: invalid escape sequence '\|'
  re_invalid_package_name = re.compile('[@!#$%^&*()<>?/\|}{~:]')

This can be fixed by making the re.compile argument a raw R'...' string,
capital R avoids issues with some Microsoft IDEs.
(Alternative is doubling the backslash, but that's less readable.)

Pull Request: https://github.com/freebsd/freebsd-ports/pull/550