Update Dockerfile

fix pip v10 error 
Traceback (most recent call last):
  File "/usr/bin/pip", line 9, in <module>
    from pip import main
ImportError: cannot import name main

workspace/Dockerfile

@@ -641,8 +641,8 @@ ARG INSTALL_PYTHON=false
 
 RUN if [ ${INSTALL_PYTHON} = true ]; then \
   apt-get -y install python python-pip python-dev build-essential  \
-  && pip install --upgrade pip  \
+  && pythom -m pip install --upgrade pip  \
-  && pip install --upgrade virtualenv \
+  && pythom -m pip install --upgrade virtualenv \
 ;fi
 
 ###########################################################################