git-remote-mediawiki: make a regexp clearer

git-remote-mediawiki: make a regexp clearer

Perl's split function takes a regex pattern argument. You can also
feed it an expression, which is then compiled into a regex at runtime.
It therefore works to pass your pattern via single quotes, but it is
much less obvious to a reader that the argument is meant to be a
regex, not a static string. Using the traditional slash-delimiters
makes this easier to read.

Signed-off-by: Célestin Matte <celestin.matte@ensimag.fr>
Signed-off-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>