add python3-all dep

Signed-off-by: Mike Marchetti <mmarchetti@sandvine.com>
diff --git a/Dockerfile b/Dockerfile
index b7a8a91..058c506 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -2,4 +2,4 @@
 
 RUN apt-get update && apt-get -y install git make python python3 \
     libcurl4-gnutls-dev libgnutls-dev tox python-dev python3-dev \
-    debhelper python-setuptools python-all apt-utils
+    debhelper python-setuptools python-all python3-all apt-utils