module: support Python 3 only

.github/workflows/ci.yml

@@ -12,14 +12,12 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
     strategy:
       matrix:
         python-version:
-        - '2.7'
-        - '3.4'
-        - '3.5'
         - '3.7'
+        - '3.8'
         - '3.9'
     steps:
     - uses: actions/checkout@v2