Issue #44 update tox

tox.ini

@@ -1,11 +1,12 @@
 # content of: tox.ini , put in same dir as setup.py
 [tox]
-envlist = py36,lint
+envlist = py37,lint
 skipsdist = True
+requires = setuptools >= 47.1
 
 [travis]
 python =
-  3.6: py36, docs, lint
+  3.7: py37, docs, lint
 
 [testenv]
 deps=-rrequirements-dev.txt
@@ -17,23 +18,23 @@ commands = coverage erase
            coverage report -m
 
 [testenv:lint]
-basepython=python3.6
+basepython=python3.7
 deps={[testenv]deps}
 commands=pylint --rcfile=tests/pylintrc sksurgerytf
 
 [testenv:docs]
-basepython=python3.6
+basepython=python3.7
 changedir=docs
 deps={[testenv]deps}
 commands = sphinx-build -M html . build
 
 [testenv:installer]
-basepython=python3.6
+basepython=python3.7
 deps={[testenv]deps}
 commands=pyinstaller --onefile sksurgeryfashion.py --noconfirm --windowed
 
 [testenv:pip3]
-basepython=python3.6
+basepython=python3.7
 changedir=pip_test
 skip_install=True
 commands = pip install {posargs}