Update Dockerfile

Dockerfile

@@ -21,7 +21,7 @@ ENV PATH $CONDA_DIR/bin:$PATH
 # Modify this section for the conda/python update.
 # This list of miniconda installer versions together with their SHA256 check sums are available:
 # https://docs.conda.io/en/latest/miniconda_hashes.html
-ENV PYTHON_VERSION py38
+ENV PYTHON_VERSION py39
 ENV CONDA_VERSION 4.12.0
 ENV MINICONDA_VERSION ${PYTHON_VERSION}_${CONDA_VERSION}