contrib/docker/debian-jessie

addrevision: rename 'd' to 'delta'

That variable is quite central to the whole function. Giving it a more explicit
name help with code readability.

FROM debian:jessie
RUN apt-get update && apt-get install -y \
  build-essential \
  debhelper \
  dh-python \
  devscripts \
  python \
  python-all-dev \
  python-docutils \
  zip \
  unzip