Bump nbclient, rm support for py3.6 (#66)

Fixes #63

Author: alex-treebeard

.github/workflows/pytest.yml

@@ -8,8 +8,6 @@ jobs:
       fail-fast: false
       matrix:
         cfg:
-          - os: ubuntu-latest
-            python-version: "3.6"
           - os: ubuntu-latest
             python-version: "3.7"
           - os: ubuntu-latest