Bump doorkeeper from 5.0.2 to 5.1.0 (mastodon#10598)

Bumps [doorkeeper](https://github.com/doorkeeper-gem/doorkeeper) from 5.0.2 to 5.1.0.
- [Release notes](https://github.com/doorkeeper-gem/doorkeeper/releases)
- [Changelog](https://github.com/doorkeeper-gem/doorkeeper/blob/master/NEWS.md)
- [Commits](doorkeeper-gem/doorkeeper@v5.0.2...v5.1.0)

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

Gemfile

@@ -42,7 +42,7 @@ gem 'omniauth-cas', '~> 1.1'
 gem 'omniauth-saml', '~> 1.10'
 gem 'omniauth', '~> 1.9'
 
-gem 'doorkeeper', '~> 5.0'
+gem 'doorkeeper', '~> 5.1'
 gem 'fast_blank', '~> 1.0'
 gem 'fastimage'
 gem 'goldfinger', '~> 2.1'

Gemfile.lock

@@ -184,8 +184,8 @@ GEM
     docile (1.3.0)
     domain_name (0.5.20180417)
       unf (>= 0.0.5, < 1.0.0)
-    doorkeeper (5.0.2)
-      railties (>= 4.2)
+    doorkeeper (5.1.0)
+      railties (>= 5)
     dotenv (2.7.2)
     dotenv-rails (2.7.2)
       dotenv (= 2.7.2)
@@ -680,7 +680,7 @@ DEPENDENCIES
   devise (~> 4.6)
   devise-two-factor (~> 3.0)
   devise_pam_authenticatable2 (~> 9.2)
-  doorkeeper (~> 5.0)
+  doorkeeper (~> 5.1)
   dotenv-rails (~> 2.7)
   fabrication (~> 2.20)
   faker (~> 1.9)