Add test with Python 3.10. (#534)

.github/workflows/build-test.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         platform: ["windows-latest", "macos-latest", "ubuntu-latest"]
-        python-version: ["3.6", "3.7", "3.8", "3.9"]
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
         exclude:
           - platform: "macos-latest"
             python-version: "3.6"

README.md

@@ -2,7 +2,7 @@
 
 [![PyPI version](https://badge.fury.io/py/uproot.svg)](https://pypi.org/project/uproot)
 [![Conda-Forge](https://img.shields.io/conda/vn/conda-forge/uproot)](https://github.com/conda-forge/uproot-feedstock)
-[![Python 2.7,3.5‒3.9](https://img.shields.io/badge/python-2.7%2C3.5%E2%80%923.9-blue)](https://www.python.org)
+[![Python 3.6‒3.10](https://img.shields.io/badge/python-3.6%E2%80%923.10-blue)](https://www.python.org)
 [![BSD-3 Clause License](https://img.shields.io/badge/license-BSD%203--Clause-blue.svg)](https://opensource.org/licenses/BSD-3-Clause)
 [![Continuous integration tests](https://img.shields.io/github/workflow/status/scikit-hep/uproot4/Test%20build/main?label=tests)](https://github.com/scikit-hep/uproot4/actions)