t/translator.t: use instance() method, not new()

Pull request zonemaster-engine#1347
(zonemaster/zonemaster-engine#1347) has been
merged, which fixes Zonemaster::Backend::Translator->instance(). So we
can remove one use of the deprecated
Zonemaster::Backend::Translator->new() in the unit tests.

t/translator.t

@@ -16,12 +16,9 @@ isa_ok 'Zonemaster::Backend::Translator', 'Zonemaster::Engine::Translator';
 
 my $translator;
 
-# FIXME: the new() method is deprecated but the instance() method does not
-# work; the following should be changed once Zonemaster::Engine::Translator
-# (Engine, not Backend) is fixed.
-$translator = Zonemaster::Backend::Translator->new();
+$translator = Zonemaster::Backend::Translator->instance();
 isa_ok $translator, 'Zonemaster::Backend::Translator',
-    "Zonemaster::Backend::Translator->new()";
+    "Zonemaster::Backend::Translator->instance()";
 
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 ### Change locale