Remove .rspec_status from the gem bundle

[rwojsznis]

• Simplify spec.files in the gemspec so package includes only required files
• Remove and add .rspec_status to .gitignore as by accident it was part of the gem

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Hey there 👋 I was looking at my CI bundle cache size as looking for biggest offenders and noticed that this gem adds unnecessary 17MB rspec status file - seems it was added by accident in #57

[rwojsznis]

Oh, seems like some test fails - probably due to rack and legacy ruby incompatibility 🤔

An error occurred while loading ./spec/rack_spec.rb.
Failure/Error: require "rack/test"

TypeError:
  wrong element type String at 0 (expected array)
# ./vendor/bundle/ruby/2.5.0/gems/rack-3.2.6/lib/rack/utils.rb:149:in `to_h'

Doesn't seems to be related to the change itself tho; this Ruby EOLed a while back so maybe there is no point of running tests on such old version 🤷 (out of scope of this PR ofc 😅 )

[loadkpi]

Oh, seems like some test fails - probably due to rack and legacy ruby incompatibility 🤔

An error occurred while loading ./spec/rack_spec.rb.
Failure/Error: require "rack/test"

TypeError:
  wrong element type String at 0 (expected array)
# ./vendor/bundle/ruby/2.5.0/gems/rack-3.2.6/lib/rack/utils.rb:149:in `to_h'

Doesn't seems to be related to the change itself tho; this Ruby EOLed a while back so maybe there is no point of running tests on such old version 🤷 (out of scope of this PR ofc 😅 )

fixed in #65

I prefer to run with old versions to make sure it has backward compability

Please make a rebase