Update dentaku requirement from = 2.0.4 to = 3.3.4

Updates the requirements on [dentaku](https://github.com/rubysolo/dentaku) to permit the latest version.
- [Release notes](https://github.com/rubysolo/dentaku/releases)
- [Changelog](https://github.com/rubysolo/dentaku/blob/master/CHANGELOG.md)
- [Commits](rubysolo/dentaku@v2.0.4...v3.3.4)

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

Author: dependabot-preview[bot]

sensu-plugins-postgres.gemspec

@@ -36,7 +36,7 @@ Gem::Specification.new do |s| # rubocop:disable Metrics/BlockLength
 
   s.add_runtime_dependency 'sensu-plugin', '~> 1.2'
 
-  s.add_runtime_dependency 'dentaku',      '2.0.4'
+  s.add_runtime_dependency 'dentaku',      '3.3.4'
   s.add_runtime_dependency 'pg',           '1.1'
 
   s.add_development_dependency 'bundler',                   '~> 1.7'