docker: fix build warnings

Author: csegarragonz

docker/faabric.dockerfile

@@ -5,7 +5,7 @@ ARG FAABRIC_VERSION
 SHELL ["/bin/bash", "-c"]
 
 # Flag to say we're in a container
-ENV FAABRIC_DOCKER "on"
+ENV FAABRIC_DOCKER="on"
 
 # Put the code in place
 WORKDIR /code
@@ -30,7 +30,7 @@ RUN ./bin/create_venv.sh \
 RUN echo "set auto-load safe-path /" > /root/.gdbinit
 
 # CLI setup
-ENV TERM xterm-256color
+ENV TERM=xterm-256color
 
 RUN echo ". /code/faabric/bin/workon.sh" >> ~/.bashrc
 CMD ["/bin/bash", "-l"]