build failing

see https://travis-ci.org/bigchaindb/cryptoconditions

```bash
==================================== ERRORS ====================================

___________________ ERROR collecting tests/test_condition.py ___________________

ImportError while importing test module '/home/travis/build/bigchaindb/cryptoconditions/tests/test_condition.py'.

Hint: make sure your test modules/packages have valid Python names.

Traceback:

tests/test_condition.py:3: in

from hypothesis_regex import regex

../../../virtualenv/python3.5.3/lib/python3.5/site-packages/hypothesis_regex.py:10: in

from hypothesis.searchstrategy.reprwrapper import ReprWrapperStrategy

E ImportError: No module named 'hypothesis.searchstrategy.reprwrapper'

!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!

=========================== 1 error in 1.24 seconds ============================
```