fix: pyethash version reqirement

Author: heikoheiko

.travis.yml

@@ -8,7 +8,7 @@ install:
   - pip install -r requirements.txt
 
 script:
-- coverage run --source pyethereum setup.py test
+- coverage run --source ethereum setup.py test
 #- tox -e $TOX_ENV
 
 after_success:

setup.py

@@ -34,7 +34,7 @@ def run_tests(self):
 install_requires_replacements = {
     'https://github.com/ethereum/pyrlp/tarball/develop': 'rlp>=0.3.7',
     'https://github.com/ethereum/serpent/tarball/develop': 'ethereum-serpent>=1.8.1',
-    'https://github.com/ethereum/ethash/tarball/master': 'pyethash>=23'}
+    'https://github.com/ethereum/ethash/tarball/master': 'pyethash'}
 
 install_requires = [install_requires_replacements.get(r, r) for r in install_requires]