Merge pull request #389 from AurelienJaquier/master

Fix syntax change from latest version of pytest

Author: wvangeit

tox.ini

@@ -38,7 +38,7 @@ commands =
     syntax: flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics
 
     unit: pytest --cov=bluepyopt {[testenv]coverage_options} bluepyopt/tests -k unit
-    functional: pytest --cov=bluepyopt {[testenv]coverage_options} bluepyopt/tests -k-unit
+    functional: pytest --cov=bluepyopt {[testenv]coverage_options} bluepyopt/tests -k 'not unit'
 
 [testenv:docs]
 basepython = python3.6