[Mattermost] Bump to 5.20.1

pica-mattermost/Dockerfile

@@ -4,7 +4,7 @@ FROM alpine:3.11
 ENV PATH="/mattermost/bin:${PATH}"
 
 # Picasoft : change these values. The team version is used by default
-ENV MM_VERSION=5.19.0
+ENV MM_VERSION=5.20.1
 # Get these ids with the output of `id mattermost` on the VM hosting the app
 ARG PUID=5000
 ARG PGID=5000