Land #14657, download version of get-pip supporting python2

Dockerfile

@@ -59,7 +59,7 @@ RUN chown -R root:metasploit $APP_HOME/
 RUN chmod 664 $APP_HOME/Gemfile.lock
 RUN gem update --system
 RUN cp -f $APP_HOME/docker/database.yml $APP_HOME/config/database.yml
-RUN curl -O https://bootstrap.pypa.io/get-pip.py && python get-pip.py && rm get-pip.py
+RUN curl -L -O https://github.com/pypa/get-pip/raw/3843bff3a0a61da5b63ea0b7d34794c5c51a2f11/get-pip.py && python get-pip.py && rm get-pip.py
 RUN pip install impacket
 
 WORKDIR $APP_HOME