🦗 Upgrade ci to TF 2.6.0

Author: dathudeptrai

.github/workflows/ci.yaml

@@ -17,7 +17,7 @@ jobs:
       max-parallel: 10
       matrix:
         python-version: [3.7]
-        tensorflow-version: [2.3.1]
+        tensorflow-version: [2.6.0]
     steps:
       - uses: actions/checkout@master
       - uses: actions/setup-python@v1