Dockerfile: Update to the bionic-20191202 tag

Move up to the latest tag to get the usual related security fixes that
brings in.

Note that this went live with the 10Jan2020 image but was not committed
at the time.

Signed-off-by: Tom Rini <trini@konsulko.com>

Dockerfile

@@ -2,7 +2,7 @@
 # This Dockerfile is used to build an image containing basic stuff to be used
 # to build U-Boot and run our test suites.
 
-FROM ubuntu:bionic-20191029
+FROM ubuntu:bionic-20191202
 MAINTAINER Tom Rini <trini@konsulko.com>
 LABEL Description=" This image is for building U-Boot inside a container"