Fix Style/HashConversion by rubocop.

[M-Yamashita01]

The following code was pointed out by Rubocop.

spec/pronto/rubocop/offense_line_spec.rb:56:13: C: [Correctable] Style/HashConversion: Prefer ary.to_h to Hash[ary].
            Hash[::RuboCop::Cop::Severity::NAMES.map { |name| [name, 'fatal'] }] 
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Therefore, we fixed the code.
Could you please approve this PR?

[ashkulz]

Thanks!