info log level in production

In rails 5.0 unified log level (when log_level is not set) is set to `:debug`:

> DEPRECATION WARNING: You did not specify a `log_level` in `production.rb`. Currently, the default value for `log_level` is `:info` for the production environment and `:debug` in all other environments. In Rails 5 the default value will be unified to `:debug` across all environments