[PATCH -perfbook 4/6] docker/Dockerfile: Use 'latest' as the default tag

[Akira Yokosawa <akiyks@xxxxxxxxx>]

ubuntu:jammy (22.04) based image works just fine for building
perfbook.  The tag of "latest" should work fine.

Signed-off-by: Akira Yokosawa <akiyks@xxxxxxxxx>
---
 docker/Dockerfile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/docker/Dockerfile b/docker/Dockerfile
index 1fec609a0043..faa0a0fb5a31 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -1,4 +1,5 @@
-FROM ubuntu:focal
+ARG rel=latest
+FROM ubuntu:$rel
 
 RUN apt-get update && apt-get install -y locales && \
     localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8 && \
-- 
2.25.1