Simplify the asyncio Tox environment

.travis.yml

@@ -16,7 +16,7 @@ matrix:
       python: 3.5
     - env: TOXENV=pinned
       python: 3.5
-    - env: TOXENV=py35-asyncio
+    - env: TOXENV=asyncio
       python: 3.5.2
     - env: TOXENV=py36
       python: 3.6
@@ -26,7 +26,7 @@ matrix:
       python: 3.8
     - env: TOXENV=extra-deps
       python: 3.8
-    - env: TOXENV=py38-asyncio
+    - env: TOXENV=asyncio
       python: 3.8
     - env: TOXENV=docs
       python: 3.7  # Keep in sync with .readthedocs.yml

tox.ini

@@ -102,16 +102,6 @@ setenv = {[docs]setenv}
 commands =
     sphinx-build -W -b linkcheck . {envtmpdir}/linkcheck
 
-[asyncio]
+[testenv:asyncio]
 commands =
     {[testenv]commands} --reactor=asyncio
-
-[testenv:py35-asyncio]
-basepython = python3.5
-deps = {[testenv]deps}
-commands = {[asyncio]commands}
-
-[testenv:py38-asyncio]
-basepython = python3.8
-deps = {[testenv]deps}
-commands = {[asyncio]commands}