Resolve Ruby 2.5 inconsistency

2.5 regarded the begin as "relevant" which we usually don't,
so I consider it a minor/not noteworthy 2.5 bug.

Ignoring the file in question, which we aren't interested in
the test coverage of should solve the problem.

features/minitest_basic.feature

@@ -4,19 +4,20 @@ Feature:
     Given SimpleCov for Minitest is configured with:
       """
       require 'simplecov'
-      SimpleCov.start
+      SimpleCov.start do
+        add_filter "test_helper.rb"
+      end
       """
 
     When I open the coverage report generated with `bundle exec rake minitest`
     Then I should see the groups:
       | name      | coverage | files |
-      | All Files | 85.71%   | 3     |
+      | All Files | 87.5%   | 2     |
 
     And I should see the source files:
       | name                                    | coverage |
       | lib/faked_project/some_class.rb         | 80.0 %   |
       | minitest/some_test.rb                   | 100.0 %  |
-      | minitest/test_helper.rb                 | 75.0 %   |
 
   Scenario:
     Given SimpleCov for Minitest is configured with: