Update zxcvbn-ruby requirement from ~> 0.1 to >= 0.1, < 2.0

Updates the requirements on [zxcvbn-ruby](https://github.com/envato/zxcvbn-ruby) to permit the latest version.
- [Release notes](https://github.com/envato/zxcvbn-ruby/releases)
- [Changelog](https://github.com/envato/zxcvbn-ruby/blob/master/CHANGELOG.md)
- [Commits](envato/zxcvbn-ruby@v0.1.0...v0.1.2)

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

session_keys.gemspec

@@ -47,7 +47,7 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency 'rbnacl', '~> 3.4.0'
   spec.add_dependency 'rbnacl-libsodium', '~> 1.0'
-  spec.add_dependency 'zxcvbn-ruby', '~> 0.1'
+  spec.add_dependency 'zxcvbn-ruby', '>= 0.1', '< 2.0'
 
   spec.add_development_dependency 'bundler'
   spec.add_development_dependency 'rake'