Update drone.yml and Dockerfile

Dockerfile

 FROM debian:stable-slim
 MAINTAINER Drone CI/CD
 
+ARG HTTP_PROXY
 RUN echo $'\n\
       Acquire::http  { Proxy "'$HTTP_PROXY$'"; } \n\
       Acquire::https { Proxy "https://"; }; \n\
 '   >> /etc/apt/apt.conf.d/01-proxy
 
+RUN ls -l /etc/apt/apt.conf.d/01-proxy
+RUN cat /etc/apt/apt.conf.d/01-proxy
+
+ARG BUILDDEPS
 RUN apt-get update && \
     apt-get --yes upgrade && \
     apt-get --yes install $BUILDDEPS