Merge ~ubuntu-docker-images/ubuntu-docker-images/+git/prometheus-alertmanager:snap-channel into ~ubuntu-docker-images/ubuntu-docker-images/+git/prometheus-alertmanager:0.21-21.04

[Sergio Durigan Junior]

Use the proper snap channel when downloading the snap, now that we have tracks for 20.04 and 21.04.

[Lucas Kanashiro (lucaskanashiro)]

LGTM, +1.

It built fine locally and the tests are passing.

review: Approve

[Sergio Durigan Junior (sergiodj)]

Thanks, Lucas. I've merged the branch.

diff --git a/Dockerfile b/Dockerfile
index 2b5caa0..28a5cba 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -7,7 +7,7 @@ RUN set -eux; \
 		jq curl ca-certificates squashfs-tools; \
 # taken from https://snapcraft.io/docs/build-on-docker
 # Alternatively, we can install snapd, and issue `snap download prometheus-alertmanager`
-	curl -L $(curl -H 'X-Ubuntu-Series: 16' 'https://api.snapcraft.io/api/v1/snaps/details/prometheus-alertmanager?channel=edge' | jq '.download_url' -r) --output prometheus-alertmanager.snap; \
+	curl -L $(curl -H 'X-Ubuntu-Series: 16' 'https://api.snapcraft.io/api/v1/snaps/details/prometheus-alertmanager?channel=21.04/edge' | jq '.download_url' -r) --output prometheus-alertmanager.snap; \
 	mkdir -p /snap; \
 	unsquashfs -d /snap/prometheus-alertmanager prometheus-alertmanager.snap