Attend to warnings shown by `rubocop --only Style/FrozenStringLiteralComment app/`

[la-ruby]

1. Fork la-ruby/silica repo to your-github-id/silica
2. git clone, and do a local setup of the rails application
3. send a PR to upstream repo (la-ruby/silica) fixing the issues
   listed by the rubocop --only Style/FrozenStringLiteralComment app/ command
4. You can use the -A "autocorrection" feature of rubocop