Dockerfile: updated ubuntu release used for builds

This patch just revs the Ubuntu release used for builds from 13.10
to 14.04.

Docker-DCO-1.1-Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> (github: cyphar)

Dockerfile

@@ -24,7 +24,7 @@
 #
 
 docker-version	0.6.1
-FROM	ubuntu:13.10
+FROM	ubuntu:14.04
 MAINTAINER	Tianon Gravi <admwiggin@gmail.com> (@tianon)
 
 # Packaged dependencies