Define the type of OpenStruct#to_h
Define the type of OpenStruct#to_h

> lib/hatenablog/configuration.rb:30:22: [error] Type `::Hatenablog::Configuration` does not have method `to_h`
> │ Diagnostic ID: Ruby::NoMethod
> │
> └       config_keys   = to_h.keys
>                         ~~~~

kymmt90/hatenablog,kymmt90/hatenablog