Update ci.yml

remove 3.6 support (reached end-of-life)

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
 
     strategy:
       matrix:
-        python: [3.6, 3.7, 3.8, 3.9]
+        python: [3.7, 3.8, 3.9]
 
     steps:
       - name: Checkout repo