Testsuite fails with Minitest 5.20

As of clockwork git head ( https://github.com/Rykian/clockwork/commit/7ed9042e49cd841e41fe516f74ffd290fcb2105f ), testsuite fails with Minitest 5.20 as:

$ ruby -Ilib:test -rclockwork -e "Dir.glob('./test/**/*_test.rb').sort.each {|t| require t}"
Loaded suite -e
Started

  1) Error:
Clockwork::Manager#test_0012_exceptions are trapped and logged:
NameError: uninitialized constant MiniTest
    /builddir/build/GIT/clockwork/test/manager_test.rb:120:in `block (2 levels) in <top (required)>'

93 runs, 168 assertions, 0 failures, 1 errors, 0 skips

Already for a long while "Minitest" usage is preferred and with 5.19 "MiniTest" usage is hidden by default.

Rykian / clockwork

Testsuite fails with Minitest 5.20 #84