Bump py39

Author: jmadler

Dockerfile

@@ -29,7 +29,7 @@ RUN PATH=/opt/pyenv/bin:$PATH pyenv install 3.7.7
 RUN virtualenv /root/py37 --python /opt/pyenv/versions/3.7.7/bin/python
 RUN PATH=/opt/pyenv/bin:$PATH pyenv install 3.8.3
 RUN virtualenv /root/py38 --python /opt/pyenv/versions/3.8.3/bin/python
-RUN PATH=/opt/pyenv/bin:$PATH pyenv install 3.9.0a6
+RUN PATH=/opt/pyenv/bin:$PATH pyenv install 3.9.0b1
 RUN virtualenv /root/py39 --python /opt/pyenv/versions/3.9.0a6/bin/python
 RUN ln -s /usr/bin/python3 /usr/bin/python
 ENV LC_ALL=C.UTF-8