Adapt use of with_indifferent_access so it works on and after rails 5.1

[renandhein]

As of rails 5.1, ActionController::Parameters drifts further away from behaving like a simple Hash and the direct use of rails' with_indifferent_access method over it that was already deprecated now causes an error.

This is a simple fix to transform received options on dossier initialization to a hash when they are ActionController::Parameters so that we can continue using with_indifferent_access and keep everything that comes afterwards working as intended.

This is the only incompatibility I've found so far using dossier in an application running on Rails 5.1.

[coveralls]

Coverage decreased (-38.2%) to 61.795% when pulling 88ae597 on renandhein:master into 81564d5 on tma1:master.

[adamhunter]

thank you for posting this! I'll do my best to get it merged in quickly.