Try pegging the version of setuptools used by tox

.travis.yml

@@ -15,6 +15,10 @@ python:
 # but not block on it)
 - '3.7-dev'
 install:
+# always install latest pip and setuptools versions on Travis
+# testing on older versions can be done manually when necessary
+- travis_retry pip install --upgrade pip
+- travis_retry pip install --upgrade setuptools
 - travis_retry pip install tox-travis
 - travis_retry pip install coveralls
 - travis_retry pip install coverage

tox.ini

@@ -4,7 +4,8 @@ envlist=py27,py33,py34,py35,py36,py37,pypy,jython,docs,pypy3
 # Default settings for py27, py33, py34 and pypy
 [testenv]
 install_command=pip install . {packages}
-depts=coverage
+deps=-r{toxinidir}/requirements.txt
+     setuptools==38.2.3
 setenv=PYTHONPATH={toxinidir}
 commands=coverage erase
          coverage run -m nose2.__main__ -v