update example Dockerfile.mqttwarn-slack to use GHCR image

sumnerboy12 · sumnerboy12 · commit 338477e53bac · 2021-10-18T10:49:19.000+13:00
diff --git a/Dockerfile.mqttwarn-slack b/Dockerfile.mqttwarn-slack
@@ -7,7 +7,7 @@
 #
 
 # Derive from upstream image.
-FROM jpmens/mqttwarn:0.23.0
+FROM ghcr.io/jpmens/mqttwarn-standard:0.27.0
 
 # Make package installation run as "root" user
 USER root

Original file line number	Diff line number	Diff line change
`@@ -7,7 +7,7 @@`
`7`	`7`	`#`
`8`	`8`
`9`	`9`	`# Derive from upstream image.`
`10`		`-FROM jpmens/mqttwarn:0.23.0`
	`10`	`+FROM ghcr.io/jpmens/mqttwarn-standard:0.27.0`
`11`	`11`
`12`	`12`	`# Make package installation run as "root" user`
`13`	`13`	`USER root`