Update rubocop to version 0.89.0 (#59)

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Update rubocop to version 0.88.0 (#57)
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(#53)
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(#47)
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Fix minor typos (#46)

- based on recommendations of https://piotrmurach.com/articles/writing-a-ruby-gem-specification/

- json was added pre Ruby 2.0 in e50430b177

- including review suggestions from @jgraichen

- https://docs.travis-ci.com/user/reference/overview/#deprecated-virtualization-environments

Update rubocop to version 0.80.0 (#44)

Update rubocop to version 0.79.0 (#43)

Update rubocop to version 0.78.0 (#42)

Update rubocop to version 0.77.0 (#41)

Update rubocop to version 0.76.0 (#40)

Update rubocop to version 0.75.0 (#39)

Update rubocop to version 0.74.0 (#37)

Update rubocop to version 0.73.0 (#36)

Update rubocop to version 0.72.0 (#35)

Update rubocop to version 0.71.0 (#34)

Update rubocop to version 0.70.0 (#33)

Update rubocop to version 0.69.0 (#32)

Update rubocop to version 0.68.0 (#31)

Update rubocop to version 0.66.0 (#29)

Update rubocop to version 0.65.0 (#28)

Update rubocop to version 0.64.0 (#27)

Update rack-tracer to version 0.9.0 (#26)

Update rubocop to version 0.63.0 (#25)

Update opentracing to version 0.5.0 (#24)