The repository 'https://developer.download.nvidia.com/compute/cuda/repos/ubuntu1804/x86_64 InRelease' is not signed.
A new key is available and can be installed in your build with the following process. Take note of the inline comments as they are important.
#fix nvidia gpg key
NOTE: when adding the additional instructions make sure the new RUN commands are executed prior to any other update operations (apt or yum), otherwise the run will fail .