This is to deal with new perl 5.22 warnings like

 Unescaped left brace in regex is deprecated, passed through in regex;
 marked by <-- HERE in m/\\nameurl{ <-- HERE (.*)}{(.*)}/
 at /usr/share/linuxdoc-tools/fmt/fmt_latex2e.pl line 287.

For consistency, right brackets are also escaped, although they
currently don't trigger any warning.
Signed-off-by: Agustin Martin Domingo <agmartin@debian.org>