remove python3.6 build

Author: mganahl

.github/workflows/ci-build.yml

@@ -12,7 +12,7 @@ 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