Bump doorkeeper from 4.4.1 to 5.0.0

Bumps [doorkeeper](https://github.com/doorkeeper-gem/doorkeeper) from 4.4.1 to 5.0.0.
- [Release notes](https://github.com/doorkeeper-gem/doorkeeper/releases)
- [Changelog](https://github.com/doorkeeper-gem/doorkeeper/blob/master/NEWS.md)
- [Upgrade guide](https://github.com/doorkeeper-gem/doorkeeper/blob/master/UPGRADE.md)
- [Commits](doorkeeper-gem/doorkeeper@v4.4.1...v5.0.0)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Gemfile.lock

@@ -97,7 +97,7 @@ GEM
     docile (1.3.1)
     domain_name (0.5.20180417)
       unf (>= 0.0.5, < 1.0.0)
-    doorkeeper (4.4.1)
+    doorkeeper (5.0.0)
       railties (>= 4.2)
     dotenv (2.5.0)
     dotenv-rails (2.5.0)