MiniTest::Unit.options has default :seed

MiniTest::Unit (superclass of Test::Unit::Runner) does not has
default seed parameter, but assigned after initializing.
However some tests use MiniTest::Unit without setup of seed option
and it cases unexpected test failures. To solve this issue, add
default seed parameter 42.

tool/lib/minitest/unit.rb

@@ -763,7 +763,7 @@ module MiniTest
     # Lazy accessor for options.
 
     def options
-      @options ||= {}
+      @options ||= {seed: 42}
     end
 
     @@installed_at_exit ||= false

tool/test/minitest/metametameta.rb

@@ -47,7 +47,6 @@ class MetaMetaMetaTestCase < MiniTest::Unit::TestCase
     srand 42
     MiniTest::Unit::TestCase.reset
     @tu = MiniTest::Unit.new
-    @tu.options[:seed] = 42
 
     MiniTest::Unit.runner = nil # protect the outer runner from the inner tests
   end