add build-essential to elf
add build-essential to elf

edurange/edurange,donkey-hotei/edurange,edurange/edurange-server,edurange/edurange,edurange/edurange-server,donkey-hotei/edurange,donkey-hotei/edurange,edurange/edurange-server,donkey-hotei/edurange,edurange/edurange-server,edurange/edurange,edurange/edurange