git-remote-mediawiki: replace :utf8 by :encoding(UTF-8)

Follow perlcritic's InputOutput::RequireEncodingWithUTF8Layer policy

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

@@ -18,8 +18,8 @@
 use warnings;
 
 # By default, use UTF-8 to communicate with Git and the user
-binmode STDERR, ":utf8";
-binmode STDOUT, ":utf8";
+binmode STDERR, ":encoding(UTF-8)";
+binmode STDOUT, ":encoding(UTF-8)";
 
 use URI::Escape;
 use IPC::Open2;
@@ -587,7 +587,7 @@ sub literal_data_raw {
 	utf8::downgrade($content);
 	binmode STDOUT, ":raw";
 	print STDOUT "data ", bytes::length($content), "\n", $content;
-	binmode STDOUT, ":utf8";
+	binmode STDOUT, ":encoding(UTF-8)";
 }
 
 sub mw_capabilities {