[Netfilter] python-tipbles 0.13.0 plus missing vars for 0.13.0

data/Dockerfiles/netfilter/Dockerfile

@@ -1,8 +1,12 @@
 FROM alpine:3.6
 LABEL maintainer "Andre Peters <andre.peters@servercow.de>"
 
+ENV XTABLES_LIBDIR /usr/lib/xtables
+ENV PYTHON_IPTABLES_XTABLES_VERSION 12
+ENV IPTABLES_LIBDIR /usr/lib
+
 RUN apk add -U python2 python-dev py-pip gcc musl-dev iptables ip6tables \
-  && pip2 install --upgrade python-iptables==0.12.0 redis ipaddress \
+  && pip2 install --upgrade python-iptables==0.13.0 redis ipaddress \
   && apk del python-dev py2-pip gcc
 
 COPY server.py /