Update Dockerfile

Dockerfile

 FROM debian:stable-slim
 
 RUN echo 'export http_proxy=$(ip route list exact 0.0.0.0/0 | head -1 | cut -d" " -f3):3142' >> /etc/profile ; \
-    source /etc/profile
+    . /etc/profile
 
 ARG BUILDDEPS
 RUN apt-get update && \