Update mongoid requirement from >= 4, < 8 to >= 4, < 10

Updates the requirements on [mongoid](https://github.com/mongodb/mongoid) to permit the latest version.
- [Release notes](https://github.com/mongodb/mongoid/releases)
- [Changelog](https://github.com/mongodb/mongoid/blob/master/CHANGELOG.md)
- [Commits](mongodb/mongoid@v4.0.0...v8.1.5)

---
updated-dependencies:
- dependency-name: mongoid
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -59,13 +59,13 @@ end
 if ENV['MONGOID_VERSION']
   case ENV['MONGOID_VERSION']
   when /^7/
-    gem 'mongoid', '~> 7'
+    gem 'mongoid', '>= 4', '< 10'
   when /^6/
-    gem 'mongoid', '~> 6'
+    gem 'mongoid', '>= 4', '< 10'
   when /^5/
-    gem 'mongoid', '~> 5'
+    gem 'mongoid', '>= 4', '< 10'
   else
-    gem 'mongoid', '>= 5'
+    gem 'mongoid', '>= 4', '< 10'
   end
 
   gem 'mongoid-locker', '~> 2.0'

devise_token_auth.gemspec

@@ -30,6 +30,6 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'sqlite3', '~> 1.4'
   s.add_development_dependency 'pg'
   s.add_development_dependency 'mysql2'
-  s.add_development_dependency 'mongoid', '>= 4', '< 8'
+  s.add_development_dependency 'mongoid', '>= 4', '< 10'
   s.add_development_dependency 'mongoid-locker', '~> 2.0'
 end