update-luarocks-packages: disable by default

Not only the binary `parallel` displays a re,inder to quote their
software but it systematically breaks update here regardless of my
network quality.
Better be slow than fail. If anyone can fix it, we may rollback this.

maintainers/scripts/update-luarocks-packages

@@ -19,7 +19,7 @@ export LUAROCKS_CONFIG="$NIXPKGS_PATH/maintainers/scripts/luarocks-config.lua"
 
 # 10 is a pretty arbitrary number of simultaneous jobs, but it is generally
 # impolite to hit a webserver with *too* many simultaneous connections :)
-PARALLEL_JOBS=10
+PARALLEL_JOBS=1
 
 exit_trap() {
     local lc="$BASH_COMMAND" rc=$?