Run `i18n-tasks checked-normalized` in Travis CI (#5443)

.travis.yml

@@ -54,4 +54,4 @@ before_script:
 script:
   - travis_retry bundle exec parallel_test spec/ --group-by filesize --type rspec
   - yarn test
-  - bundle exec i18n-tasks unused
+  - bundle exec i18n-tasks check-normalized && bundle exec i18n-tasks unused