fix: reinstate i18n fallbacks

Before i18n v1.1.0, i18n.fallbacks would eventually hit your
default_locale. That was changed without warning and broke
everything ruby-i18n/i18n#415. This restores the
previous behavior by explicity falling back to English.

config/initializers/i18n.rb

@@ -8,6 +8,8 @@
                       .map { |fname| File.basename fname, '.yml' }
                       .map(&:to_sym)
   config.i18n.available_locales = ([:en] + available_locales).uniq
+
+  config.i18n.fallbacks = %i[en]
 end
 
 module Translation