Removed superfluous `do`

See https://github.com/marick/Midje/pull/228#discussion-diff-5308658 and
the following thread for reference.

* src/midje/emission/plugins/tap.clj:

Signed-off-by: giorgio-v <giorgio@refactor.it>
Merge pull request #230 from giorgio-v/tap-superfluous-do-fix

Removed superfluous `do`