Do not freeze string from SecureRandom.hex
Do not freeze string from SecureRandom.hex

It can be ambitious error from AD session store:

    RuntimeError (can't modify frozen String):
        actionpack (4.2.7.1) lib/action_dispatch/middleware/session/abstract_store.rb:29:in `encode!'
        actionpack (4.2.7.1) lib/action_dispatch/middleware/session/abstract_store.rb:29:in `generate_sid'
        actionpack (4.2.7.1) lib/action_dispatch/middleware/session/cookie_store.rb:100:in `persistent_session_id!'
        actionpack (4.2.7.1) lib/action_dispatch/middleware/session/cookie_store.rb:74:in `block in load_session'
        actionpack (4.2.7.1) lib/action_dispatch/middleware/session/abstract_store.rb:51:in `stale_session_check!'
        actionpack (4.2.7.1) lib/action_dispatch/middleware/session/cookie_store.rb:72:in `load_session'
        actionpack (4.2.7.1) lib/action_dispatch/request/session.rb:180:in `load!'
        actionpack (4.2.7.1) lib/action_dispatch/request/session.rb:176:in `load_for_write!'
        actionpack (4.2.7.1) lib/action_dispatch/request/session.rb:129:in `delete'

https://github.com/rails/rails/blob/v4.2.7.1/actionpack/lib/action_dispatch/middleware/session/abstract_store.rb#L28-L29

taiki45/aws-xray,taiki45/aws-xray