style: corrected some style errors identified by rubocop

test/lib/rubycritic/learning/churn_gem_learning_test.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test_helper'
 require 'churn'
 require 'churn/calculator'
@@ -10,12 +12,12 @@
       minimum_churn_count: 1     # Minimum number of changes to consider a file
     }
     Churn::GitAnalyzer.stubs(:supported?).returns(true)
-    churn_calculator = ::Churn::ChurnCalculator.new(config)
+    churn_calculator = Churn::ChurnCalculator.new(config)
     report = churn_calculator.report(false)
 
     changes = report[:churn][:changes].first
 
     assert_equal 'CHANGELOG.md', changes[:file_path]
-    assert changes[:times_changed].positive?
+    assert_predicate changes[:times_changed], :positive?
   end
 end