update i18n interpolation fallback to use renamed method

lib/i18n_interpolation_fallbacks.rb

@@ -2,7 +2,7 @@ module I18n
   module Backend
     module InterpolationFallbacks
       def translate(locale, key, options = {})
-        default = extract_string_or_lambda_default!(options) if options[:default]
+        default = extract_non_symbol_default!(options) if options[:default]
         options.merge!(:default => default) if default
 
         I18n.fallbacks[locale].each do |fallback|
@@ -18,4 +18,4 @@ module I18n
       end
     end
   end
-end
+end
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