Fix password reset

Seeing this error in production.

A TypeError occurred in password_expired#update:

  can't convert Symbol into String

activesupport (3.2.17) lib/active_support/dependencies.rb:251:in `require'
  activesupport (3.2.17) lib/active_support/dependencies.rb:251:in `block in require'
  activesupport (3.2.17) lib/active_support/dependencies.rb:236:in `load_dependency'
  activesupport (3.2.17) lib/active_support/dependencies.rb:251:in `require'
  devise_security_extension (0.8.0) app/controllers/devise/password_expired_controller.rb:27:in `resource_params'
  devise_security_extension (0.8.0) app/controllers/devise/password_expired_controller.rb:14:in `update'
  actionpack (3.2.17) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
  actionpack (3.2.17) lib/abstract_controller/base.rb:167:in `process_action'
  actionpack (3.2.17) lib/action_controller/metal/rendering.rb:10:in `process_action'
  ac
Merge pull request #203 from alphagov/password-reset

Fix password reset