Removed python 3.9 from CI. See AcademySoftwareFoundation#828 for mor…

…e context about the Python 3.9.0/pybind11 bug.

.github/workflows/python-package.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [2.7, 3.7, 3.8, 3.9]
+        python-version: [2.7, 3.7, 3.8]
 
     steps:
     - uses: actions/checkout@v2

README.md

@@ -4,7 +4,7 @@ OpenTimelineIO
 ==============
 
 [![Supported VFX Platform Versions](https://img.shields.io/badge/vfx%20platform-2016--2020-lightgrey.svg)](http://www.vfxplatform.com/)
-![Supported Versions](https://img.shields.io/badge/python-2.7%2C%203.7%2C%203.8%2C%203.9-blue.svg)
+![Supported Versions](https://img.shields.io/badge/python-2.7%2C%203.7%2C%203.8-blue.svg)
 [![Build Status](https://travis-ci.com/PixarAnimationStudios/OpenTimelineIO.svg?branch=master)](https://travis-ci.com/PixarAnimationStudios/OpenTimelineIO)
 [![codecov](https://codecov.io/gh/PixarAnimationStudios/OpenTimelineIO/branch/master/graph/badge.svg)](https://codecov.io/gh/PixarAnimationStudios/OpenTimelineIO)
 [![docs](https://readthedocs.org/projects/opentimelineio/badge/?version=latest)](https://opentimelineio.readthedocs.io/en/latest/index.html)