Add Nova 5 Support

[grantholle]

There are no breaking changes to allow Nova 5 support. Would appreciate a quick tag to publish the latest version. Fixes #6

In the meantime, you can add Nova 5 support by modifying your composer.json:

Add the repo as a repository:

"repositories": [
  {
    "type": "composer",
    "url": "https://nova.laravel.com"
  },
  {
    "type": "vcs",
    "url": "https://github.com/grantholle/nova-logo-url"
  }
]

Set the version to be @dev:

"formfeed-uk/nova-logo-url": "@dev",