fix: resolve rubocop errors in instrumentation generators

[ymtdzzz]

closes: #1332

This PR solves rubocop errors in the codes generated from bin/instrumentation_generator.

Test

❯ bin/instrumentation_generator sample_package
❯ cd instrumentation/sample_package
❯ bundle install
❯ bundle exec rake rubocop
Running RuboCop...
Inspecting 11 files
...........
                                                                                                                                                                                                                                                                                                                     
11 files inspected, no offenses detected
                                                                                                                                                                                                                                                                                                                     
Tip: Based on detected gems, the following RuboCop extension libraries might be helpful:
  * rubocop-minitest (https://rubygems.org/gems/rubocop-minitest)
  * rubocop-rake (https://rubygems.org/gems/rubocop-rake)
                                                                                                                                                                                                                                                                                                                     
You can opt out of this message by adding the following to your config (see https://docs.rubocop.org/rubocop/extensions.html#extension-suggestions for more options):
  AllCops:
    SuggestExtensions: false

[plantfansam]

Makes sense!

[kaylareopelle]

Thank you!