Fix ansible-lint errors

[bahaynes]

The following errors propagate up to a playbook that lists this role as a dependency when running ansible-lint:

risky-file-permissions: File permissions unset or incorrect
../../../../../root/.cache/ansible-lint/aafa07/roles/nvidia.nvidia_docker/tasks/main.yml:2 Task/Handler: ensure facts directory exists
var-spacing: Variables should have spaces before and after: {{proxy_env if proxy_env is defined else {}}}
../../../../../root/.cache/ansible-lint/aafa07/roles/nvidia.nvidia_docker/tasks/main.yml:51 Task/Handler: grab nvidia-docker wrapper
var-spacing: Variables should have spaces before and after: {{proxy_env if proxy_env is defined else {}}}
../../../../../root/.cache/ansible-lint/aafa07/roles/nvidia.nvidia_docker/tasks/redhat-pre-install.yml:10 Task/Handler: add repo
var-spacing: Variables should have spaces before and after: {{proxy_env if proxy_env is defined else {}}}
../../../../../root/.cache/ansible-lint/aafa07/roles/nvidia.nvidia_docker/tasks/redhat-pre-install.yml:21 Task/Handler: install packages
var-spacing: Variables should have spaces before and after: {{proxy_env if proxy_env is defined else {}}}
../../../../../root/.cache/ansible-lint/aafa07/roles/nvidia.nvidia_docker/tasks/ubuntu-pre-install.yml:11 Task/Handler: add key
var-spacing: Variables should have spaces before and after: {{proxy_env if proxy_env is defined else {}}}
../../../../../root/.cache/ansible-lint/aafa07/roles/nvidia.nvidia_docker/tasks/ubuntu-pre-install.yml:18 Task/Handler: add repo
var-spacing: Variables should have spaces before and after: {{proxy_env if proxy_env is defined else {}}}
../../../../../root/.cache/ansible-lint/aafa07/roles/nvidia.nvidia_docker/tasks/ubuntu-pre-install.yml:28 Task/Handler: install packages