Linked_list_allocator Error


On trying to compile the firmware/app using the instructions and scripts provided at:

I get to the point of building the app using the below:
board=nrf52840_mdk_usb_dongle ./ app

And keep getting an issue when compiling linked_list_allocator v0.6.6, as it returns the below:
error[E0432]: unresolved import alloc::alloc::AllocRef
–> /root/.cargo/registry/src/
14 | use alloc::alloc::{AllocRef, AllocErr, Layout};
| ^^^^^^^^ no AllocRef in alloc

error: aborting due to previous error

As this library won’t compile the process aborts. I am running Ubuntu 19.10 and have the prerequesite as per the provided documentation installed. Any suggestions on what I couild do to resolve this would be welcome.

Thanks in advance.