detect-environment: Don't look for a 1-digit major release number

There has not been a 1-digit major release of ubuntu for a long time.
Hence, there is no point in looking for it when verifying the version
number extracted from /etc/lsb-release.

Ticket: ENT-12600
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

build-scripts/detect-environment

@@ -183,7 +183,7 @@ detect_distribution()
     REL=$(grep DISTRIB_RELEASE= /etc/lsb-release)
     REL=${REL#DISTRIB_RELEASE=}
     case "$REL" in
-      [0-9].[0-9][0-9]|[0-9][0-9].[0-9][0-9])
+      [0-9][0-9].[0-9][0-9])
         ;;
       *)
         echo "Unknown Ubuntu release: $REL"