lila.sh minor improvement

fix script sourced logic: return, not exit. Calling exit
terminates the "parent" shell.

lila.sh

@@ -7,11 +7,14 @@
 # Then in the sbt console:
 # run
 
+if [[ "${BASH_SOURCE[0]}" != "$0" ]]; then
+  >&2 echo "Fatal: lila.sh should be run, not sourced!"
+  return 1
+fi
+
 WARN() { >&2 printf '%s\n' "[warning] $*"; }
 ABORT() { >&2 printf '%s\n' "[FATAL] $*"; exit 1; }
 
-[[ "${BASH_SOURCE[0]}" == "$0" ]] || ABORT "should not be sourced!"
-
 cd "$(dirname -- "$0")"  # set cwd
 
 cat << 'BANNER'