Build fails with python3 about docker-readthedocs HOT 6 OPEN

#FROM debian:stretch-slim
FROM readthedocs/build:3.0

docker-compose down
docker-compose up

Traceback (most recent call last):
  File "/app/readthedocs/doc_builder/environments.py", line 150, in run
    env=environment,
  File "/usr/lib/python2.7/subprocess.py", line 390, in __init__
    errread, errwrite)
  File "/usr/lib/python2.7/subprocess.py", line 1024, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

Collecting pypandoc (from -r requirements.txt (line 1))
  Downloading https://files.pythonhosted.org/packages/71/81/00184643e5a10a456b4118fc12c96780823adb8ed974eb2289f29703b29b/pypandoc-1.4.tar.gz
Collecting pydna (from -r requirements.txt (line 2))
  Using cached https://files.pythonhosted.org/packages/67/f2/552bd375666bb3e2ff4b3ec418ed2d5bbe1140847075d7c2d682435153c8/pydna-2.0.3.zip
    Complete output from command python setup.py egg_info:
    warning: pypandoc module not found, could not convert Markdown to RST
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-ISii8l/pydna/setup.py", line 20, in <module>
        with open("README.md", encoding="utf-8") as f:
    TypeError: 'encoding' is an invalid keyword argument for this function
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-ISii8l/pydna/
You are using pip version 9.0.3, however version 19.0.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.