Simplify tox file

tox.ini

@@ -5,6 +5,13 @@ skip_missing_interpreters = true
 [testenv]
 whitelist_externals = rm
 
+[testenv:py{35,36,37}]
+commands=
+ rm -rf ./yala.egg-info/
+ pip install -U pip
+ pip install -U .[all,dev]
+ python setup.py test
+
 [testenv:py38]
 ; Code checks and linters are run in the latest Python version only.
 parallel_show_output = true
@@ -42,24 +49,3 @@ commands=
  coveralls
  codecov
  python-codacy-coverage -r coverage.xml
-
-[testenv:py37]
-commands=
- rm -rf ./yala.egg-info/
- pip install -U pip
- pip install -U .[all,dev]
- python setup.py test
-
-[testenv:py36]
-commands=
- rm -rf ./yala.egg-info/
- pip install -U pip
- pip install -U .[all,dev]
- python setup.py test
-
-[testenv:py35]
-commands=
- rm -rf ./yala.egg-info/
- pip install -U pip
- pip install -U .[all,dev]
- python setup.py test