Consider upgrading to `debian:buster`

[mmastrac]

I've tested the following change locally as it gives access to updated versions of libnice etc:

diff --git a/Dockerfile b/Dockerfile
index 1dc36ef..fc038e8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -4,7 +4,7 @@
 ############################################################

 # set base image debian jessie
-FROM debian:jessie
+FROM debian:buster

 # file maintainer author
 MAINTAINER brendan jocson <brendan@jocson.eu>
@@ -82,9 +82,9 @@ RUN \
     && DEBIAN_FRONTEND=noninteractive apt-get update \
     && DEBIAN_FRONTEND=noninteractive apt-get -y --no-install-recommends install $JANUS_BUILD_DEPS_DEV ${JANUS_BUILD_DEPS_EXT} \
 # build libsrtp
-    && curl -fSL https://github.com/cisco/libsrtp/archive/v2.0.0.tar.gz -o ${BUILD_SRC}/v2.0.0.tar.gz \
-    && tar xzf ${BUILD_SRC}/v2.0.0.tar.gz -C ${BUILD_SRC} \
-    && cd ${BUILD_SRC}/libsrtp-2.0.0 \
+    && curl -fSL https://github.com/cisco/libsrtp/archive/v2.1.0.tar.gz -o ${BUILD_SRC}/v2.1.0.tar.gz \
+    && tar xzf ${BUILD_SRC}/v2.1.0.tar.gz -C ${BUILD_SRC} \
+    && cd ${BUILD_SRC}/libsrtp-2.1.0 \
     && ./configure --prefix=/usr --enable-openssl \
     && make shared_library \
     && make install \

[dacaga]

I had opened a PR using Debian Stretch going in the same direction! #13