the working directory may not be srcdir

* test/runner.rb (COVERAGE): should use require_relative instead of require,
  because the working directory may not be srcdir.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59773 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/runner.rb

@@ -26,7 +26,7 @@ require_relative 'lib/zombie_hunter'
 require_relative 'lib/iseq_loader_checker'
 
 if ENV['COVERAGE']
-  require "tool/test-coverage.rb"
+  require_relative "../tool/test-coverage.rb"
 end
 
 begin