dup translations right after lookup in I18n::Backend::Base. based on …

…a suggestion from Erik Andrejko, https://gist.github.com/31e5aa46c8d5544df994

lib/i18n/backend/base.rb

@@ -117,7 +117,7 @@ def lookup(locale, key, scope = [], options = {})
             return nil unless result.is_a?(Hash) && result.has_key?(key)
             result = result[key]
             result = resolve(locale, key, result, options) if result.is_a?(Symbol)
-            result
+            String === result ? result.dup : result
           end
         end