Try only pytest 3.0

Author: nicoddemus

.github/workflows/main.yml

@@ -14,17 +14,17 @@ jobs:
         os: [ubuntu-latest, windows-latest]
         include:
           - python: "2.7"
-            tox_env: "py27-pytest31"
+            tox_env: "py27-pytest30"
           - python: "3.5"
-            tox_env: "py35-pytest31"
+            tox_env: "py35-pytest30"
           - python: "3.6"
-            tox_env: "py36-pytest31"
+            tox_env: "py36-pytest30"
           - python: "3.7"
-            tox_env: "py37-pytest31"
+            tox_env: "py37-pytest30"
           - python: "3.8"
-            tox_env: "py38-pytest31"
+            tox_env: "py38-pytest30"
           - python: "pypy3"
-            tox_env: "pypy3-pytest31"
+            tox_env: "pypy3-pytest30"
 
     steps:
     - uses: actions/checkout@v1