Use right lsb_release argument for HWE kernel name (-sc -> bionic, need -sr -> 18.04).

debian/changelog

@@ -2,6 +2,8 @@ livecd-rootfs (2.551) UNRELEASED; urgency=medium
 
   * Do no install openssh-server in the base filsystem for the live server
     installer.
+  * Use right lsb_release argument for HWE kernel name (-sc -> bionic, need
+    -sr -> 18.04).
 
  -- Michael Hudson-Doyle <michael.hudson@ubuntu.com>  Mon, 17 Dec 2018 13:40:21 +1300
 

live-build/ubuntu-server/hooks/033-kernel-bits.binary

@@ -35,7 +35,7 @@ for variant in $variants; do
 		kernel_metapkg=linux-generic
 		flavor=generic
 	elif [ "$variant" = "hwe" ]; then
-		kernel_metapkg=linux-generic-hwe-$(lsb_release -sc)
+		kernel_metapkg=linux-generic-hwe-$(lsb_release -sr)
 		flavor=generic-hwe
 	else
 		echo "bogus variant: $variant"