[devdocsgjs/alpine-stage-repo] Dockerfile: specify the repository to fetch the ruby-alpine image

[Andy Holmes <andyholmes src gnome org>]

commit 6226f34c1d3fb3febda9b5dcf1e9d9c89bb28523
Author: Andy Holmes <andrew g r holmes gmail com>
Date:   Tue Mar 30 23:29:43 2021 -0700

    Dockerfile: specify the repository to fetch the ruby-alpine image

 Dockerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/Dockerfile b/Dockerfile
index 639d1c10..e7406555 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -104,7 +104,7 @@ RUN for docset in appindicator301 appstreamglib10 atk10 atspi20 cairo10 \
 # - Copy from the build-stage image instead of the current dir
 # - Download only the css and javascript docsets instead of everything
 
-FROM ruby:2.7.2-alpine
+FROM docker.io/library/ruby:2.7.2-alpine
 
 ENV LANG=C.UTF-8