test fails with ruby >= 2.3

[Mr-Tao]

rake test

Run options: --seed 64681

# Running:

...................Use assert_nil if expecting nil from /trollop/test/trollop/parser_test.rb:393:in `test_short_options_combine'. This will fail in MT6.
Use assert_nil if expecting nil from /trollop/test/trollop/parser_test.rb:398:in `test_short_options_combine'. This will fail in MT6.
...................F......................E.............................................................

Finished in 0.118530s, 1037.7120 runs/s, 3729.0138 assertions/s.

  1) Failure:
Trollop::ParserTest#test_date_arg_type [/trollop/test/trollop/parser_test.rb:909]:
--- expected
+++ actual
@@ -1 +1 @@
-#<Date: 2010-05-01 ((2455318j,0s,0n),+0s,2299161j)>
+#<Date: 2010-01-05 ((2455202j,0s,0n),+0s,2299161j)>



  2) Error:
Trollop::ParserTest#test_date_formatting:
Trollop::CommandlineError: option '-d' needs a date
    /trollop/lib/trollop.rb:356:in `rescue in parse_date_parameter'
    /trollop/lib/trollop.rb:348:in `parse_date_parameter'
    /trollop/lib/trollop.rb:316:in `block (3 levels) in parse'
    /trollop/lib/trollop.rb:316:in `map'
    /trollop/lib/trollop.rb:316:in `block (2 levels) in parse'
    /blah/trollop/lib/trollop.rb:316:in `map'
    /blah/trollop/lib/trollop.rb:316:in `block in parse'
    /blah/trollop/lib/trollop.rb:293:in `each'
    /blah/trollop/lib/trollop.rb:293:in `parse'
    /blah/trollop/test/trollop/parser_test.rb:494:in `test_date_formatting'

123 runs, 442 assertions, 1 failures, 1 errors, 0 skips
rake aborted!
Command failed with status (1)
/usr/local/lib/ruby/gems/2.4.0/gems/rake-12.0.0/exe/rake:27:in `<top (required)>'
Tasks: TOP => test
(See full trace by running task with —trace)