Test with python 3.8 (#186)

Co-authored-by: Keigo Kawamura <kkawamura@preferred.jp>

Author: tdamsma

.travis.yml

@@ -23,20 +23,25 @@ jobs:
     script: |
       set -e
       pytest
+  - name: "run test suite with python 3.8"
+    python: 3.8
+    script: |
+      set -e
+      pytest
   - name: "run typecheck on stubs"
-    python: 3.7
+    python: 3.8
     script: |
       set -e
       mkdir tmpd
       cp -r sqlalchemy-stubs tmpd/sqlalchemy
       cd tmpd
       python3 -m mypy -p sqlalchemy
   - name: "run flake8 on stubs"
-    python: 3.7
+    python: 3.8
     script: |
       flake8 sqlalchemy-stubs
   - name: "run typecheck on plugin"
-    python: 3.7
+    python: 3.8
     script: |
       set -e
       MYPYPATH=external/mypy python3 -m mypy --config-file external/mypy/mypy_self_check.ini sqlmypy.py