Add lts tag

Non-LTS releases of HAProxy are only supported ~1.5 years vs. ~5 years for
non-LTS releases.

Author: TimWolla

generate-stackbrew-library.sh

@@ -3,6 +3,7 @@ set -Eeuo pipefail
 
 declare -A aliases=(
 	[1.9]='1'
+	[2.0]='lts'
 	[2.1]='latest'
 )