* pip upgrade on workspace

https://stackoverflow.com/a/65896996

dockerfiles/workspace/Dockerfile

@@ -203,7 +203,7 @@ ARG INSTALL_PYTHON=false
 
 RUN if [ ${INSTALL_PYTHON} = true ]; then \
   apt-get -y install python python-pip python-dev build-essential  \
-  && python -m pip install --upgrade pip  \
+  && python -m pip install --upgrade "pip < 21.0"  \
   && python -m pip install --upgrade virtualenv \
 ;fi