Update fastai to latest version

[kurianbenoy]

• The fastai version is a bit outdated(2.2.7, while current version is 2.4.1). Can you please update to the latest version along with pytorch upgrade planned Update pytorch from 1.7.0 to 1.8.1 #984

[rosbo]

Hi @kurianbenoy,

I am waiting on one package to support CUDA 11.1+ to upgrade pytorch to 1.8.1 and fastai will be updated to the latest version in the same upgrade.

Thank you

[roboserg]

Waiting for fastai 2.5. as well, can not submit my code with the no internet competition.

[rosbo]

Upgraded in #1083.