Fix wrong expression in spec of Collector
Fix wrong expression in spec of Collector

spec of Collector
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- Fix the wrong expression 'an instance of' to 'a kind of'.
  - At the describe 'returns an instance of Collector'.
  - In the above, at the shared examples 'to return an instance of Collector'.

indeep-xyz/ruby-insensitive-search,indeep-xyz/ruby-insensitive-search