Bug 6679 - [SIGNED-OFF] fix 4 perlcritic violations in C4/Installer.pm

Bug 6679 - [SIGNED-OFF] fix 4 perlcritic violations in C4/Installer.pm

- Bareword file handle opened at line 157, column 13.  See pages 202,204 of
PBP.  (Severity: 5)

- I/O layer ":utf8" used at line 157, column 13.  Use ":encoding(UTF-8)" to get strict validation.  (Severity: 5)

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
http://perldoc.perl.org/functions/open.html
    open(my $fh, "<:encoding(UTF-8)", "filename")
        || die "can't open UTF-8 encoded filename: $!";

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>