add django-auth-ldap to Dockerfile

Dockerfile

@@ -5,7 +5,10 @@ WORKDIR /opt/netbox
 ARG BRANCH=master
 ARG URL=https://github.com/digitalocean/netbox.git
 RUN git clone --depth 1 $URL -b $BRANCH .  && \
-	pip install gunicorn==17.5 && pip install -r requirements.txt
+    apt-get update -qq && apt-get install -y libldap2-dev libsasl2-dev libssl-dev && \
+	pip install gunicorn==17.5 && \
+	pip install django-auth-ldap && \
+    pip install -r requirements.txt
 
 ADD docker/docker-entrypoint.sh /docker-entrypoint.sh
 ADD netbox/netbox/configuration.docker.py /opt/netbox/netbox/netbox/configuration.py