deps: Bump medley to 1.4.0

[stevejmp]

Fixes #21

• The Medley update that fixes this warning landed late last night
• All tests pass:

  $ lein test-all
  Performing task 'test' with profile(s): '1.9'
  # <snip>
  Ran 45 tests containing 297 assertions.
  0 failures, 0 errors.
  Performing task 'test' with profile(s): '1.10'
  # <snip>
  Ran 45 tests containing 297 assertions.
  0 failures, 0 errors.
  Performing task 'test' with profile(s): '1.10.3'
  # <snip>
  Ran 45 tests containing 297 assertions.
  0 failures, 0 errors.