Update Docker files

[evroon]

The Dockerfile in docker/standalone/gpu still uses Ubuntu 14.04, which is quite outdated. It would be useful to update these to Ubuntu 20.04. Also, the Dockerfile currently does not work, I get the following error when building the image:

Err https://developer.download.nvidia.com  Packages
  gnutls_handshake() failed: Handshake failed
Get:24 http://archive.ubuntu.com trusty/multiverse amd64 Packages [169 kB]
Err https://developer.download.nvidia.com  Packages
  gnutls_handshake() failed: Handshake failed
W: Failed to fetch https://developer.download.nvidia.com/compute/cuda/repos/ubuntu1404/x86_64/Packages  gnutls_handshake() failed: Handshake failed

W: Failed to fetch https://developer.download.nvidia.com/compute/machine-learning/repos/ubuntu1404/x86_64/Packages  gnutls_handshake() failed: Handshake failed

E: Some index files failed to download. They have been ignored, or old ones used instead.

It seems that fetching the cuda repo using HTTPS does not work on Ubuntu 14.04, as discussed here.

[evroon]

Sorry, I was talking about your original liteflownet repo, where you have for example this Dockerfile: https://www.github.com/twhui/LiteFlowNet/tree/master/docker%2Fstandalone%2Fgpu%2FDockerfile

[twhui]

The docker folder is from FlowNet (https://github.com/lmb-freiburg/flownet2). I didn't use it. You may simply ignore it.

[evroon]

Ah okay. Thanks!