fix tox

Author: pipermerriam

.travis.yml

@@ -20,9 +20,9 @@ install:
   - travis_retry pip install coverage
 script:
   - if [ -d ".tox/$TOX_ENV/" ]; then cd ".tox/$TOX_ENV" && coverage erase"; fi;
-  - tox -e $TOX_ENV --ignore ethereum/tests/test_vm.py --ignore ethereum/tests/test_state.py
-  - tox -e $TOX_ENV ethereum/tests/test_vm.py
-  - tox -e $TOX_ENV ethereum/tests/test_state.py
+  - tox -e $TOX_ENV -- --ignore ethereum/tests/test_vm.py --ignore ethereum/tests/test_state.py
+  - tox -e $TOX_ENV -- ethereum/tests/test_vm.py
+  - tox -e $TOX_ENV -- ethereum/tests/test_state.py
   - cd .tox/$TOX_ENV && coverage report --show-missing
 after_success:
   - travis_retry pip install coveralls