Drop support to old pytest versions and test with python 3.7

tox.ini

@@ -1,30 +1,17 @@
 [tox]
-# if you change the envlist, please update .travis.yml file as well
 envlist=
   linting
-  py{27,34,35,36}-pytest{30,31,32,33,latest}
-  py{27,36}-pytest36-pexpect
+  py{27,34,35,36,37}-pytestlatest
   py{27,36}-pytest{master,features}
 
-
 [testenv]
 changedir=testing
 passenv = USER USERNAME
 deps =
-  pycmd
-  # to avoid .eggs
-  setuptools_scm
-  pytest30: pytest~=3.0.5
-  pytest31: pytest~=3.1.0
-  pytest32: pytest~=3.2.0
-  pytest33: pytest~=3.3.0
   pytestlatest: pytest
   pytestmaster: git+https://github.com/pytest-dev/pytest.git@master
   pytestfeatures: git+https://github.com/pytest-dev/pytest.git@features
-  pexpect: pexpect
   filelock
-platform=
-  pexpect: linux|darwin
 commands=
   pytest {posargs}
 
@@ -48,7 +35,7 @@ commands =
     towncrier --version {posargs} --yes
 
 [pytest]
-addopts = -rsfxX
+addopts = -ra
 
 [flake8]
 max-line-length = 120