Use safe navigation operator to avoid method calls for nil
Use safe navigation operator to avoid method calls for nil

> lib/hatenablog/entry.rb:167:61: [error] Type `(::Time | nil)` does not have method `iso8601`
> │ Diagnostic ID: Ruby::NoMethod
> │
> └         @document.at_css('entry updated').content = @updated.iso8601
                                                               ~~~~~~~

kymmt90/hatenablog,kymmt90/hatenablog