dropped python 3.6 for worflows

Author: sdushantha

.github/workflows/main.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.7, 3.8]
 
     steps:
     - uses: actions/checkout@v2

.github/workflows/nightly.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.6]
+        python-version: [3.8]
 
     steps:
     - uses: actions/checkout@v2