Update setup.cfg

Author: oesteban

setup.cfg

@@ -30,6 +30,7 @@ install_requires =
 test_requires =
     pytest
     pytest-cov
+    pytest-env
     nose
     codecov
 setup_requires =
@@ -46,6 +47,7 @@ niftiexts =
 test =
     pytest
     pytest-cov
+    pytest-env
     codecov
 tests =
     %(test)s