git-remote-mediawiki: move "use warnings;" before any instruction

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>

contrib/mw-to-git/git-remote-mediawiki.perl

@@ -15,6 +15,7 @@
 use MediaWiki::API;
 use Git;
 use DateTime::Format::ISO8601;
+use warnings;
 
 # By default, use UTF-8 to communicate with Git and the user
 binmode STDERR, ":utf8";
@@ -23,8 +24,6 @@
 use URI::Escape;
 use IPC::Open2;
 
-use warnings;
-
 # Mediawiki filenames can contain forward slashes. This variable decides by which pattern they should be replaced
 use constant SLASH_REPLACEMENT => "%2F";