Update webmock requirement from ~> 3.16.2 to ~> 3.25.0

Updates the requirements on [webmock](https://github.com/bblimke/webmock) to permit the latest version.
- [Release notes](https://github.com/bblimke/webmock/releases)
- [Changelog](https://github.com/bblimke/webmock/blob/master/CHANGELOG.md)
- [Commits](bblimke/webmock@v3.16.2...v3.25.0)

---
updated-dependencies:
- dependency-name: webmock
  dependency-version: 3.25.0
  dependency-type: direct:development
...

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

Author: dependabot[bot]

fog-openstack.gemspec

@@ -37,5 +37,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rubocop'
   spec.add_development_dependency 'shindo',  '~> 0.3'
   spec.add_development_dependency 'vcr'
-  spec.add_development_dependency 'webmock',  '~> 3.16.2'
+  spec.add_development_dependency 'webmock',  '~> 3.25.0'
 end