Update rbnacl requirement from ~> 3.4.0 to >= 3.4, < 7.1

Updates the requirements on [rbnacl](https://github.com/crypto-rb/rbnacl) to permit the latest version.
- [Release notes](https://github.com/crypto-rb/rbnacl/releases)
- [Changelog](https://github.com/crypto-rb/rbnacl/blob/master/CHANGES.md)
- [Commits](RubyCrypto/rbnacl@v3.4.0...v3.4.0)

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

session_keys.gemspec

@@ -45,7 +45,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
-  spec.add_dependency 'rbnacl', '~> 3.4.0'
+  spec.add_dependency 'rbnacl', '>= 3.4', '< 7.1'
   spec.add_dependency 'rbnacl-libsodium', '~> 1.0'
   spec.add_dependency 'zxcvbn-ruby', '>= 0.1', '< 2.0'