use non-dev py3.8

Author: willmcgugan

.travis.yml

@@ -8,17 +8,17 @@ python:
   - "3.5"
   - "3.6"
   - "3.7"
-  - "3.8-dev"
-  - 'pypy'
-  - 'pypy3.5-7.0'  # Need 7.0+ due to a bug in earlier versions that broke our tests.
+  - "3.8"
+  - "pypy"
+  - "pypy3.5-7.0" # Need 7.0+ due to a bug in earlier versions that broke our tests.
 
 matrix:
   include:
     - name: "Type checking"
       python: "3.7"
       env: TOXENV=typecheck
-    - name: 'Lint'
-      python: '3.7'
+    - name: "Lint"
+      python: "3.7"
       env: TOXENV=lint
 
   # Temporary bandaid for https://github.com/PyFilesystem/pyfilesystem2/issues/342