Update elasticsearch requirement from ~> 1.0.14 to >= 1.0.14, < 6.2.0

Updates the requirements on [elasticsearch](https://github.com/elasticsearch/elasticsearch-ruby) to permit the latest version.
- [Release notes](https://github.com/elasticsearch/elasticsearch-ruby/releases)
- [Changelog](https://github.com/elastic/elasticsearch-ruby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/elasticsearch/elasticsearch-ruby/commits/v1.1.3)

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

Author: dependabot-support

sensu-plugins-elasticsearch.gemspec

@@ -34,7 +34,7 @@ Gem::Specification.new do |s| # rubocop:disable Metrics/BlockLength
 
   s.add_runtime_dependency 'aws-es-transport', '~> 0.1'
   s.add_runtime_dependency 'aws-sdk', ['>= 2.1.14', '< 2.5', '~> 2.1']
-  s.add_runtime_dependency 'elasticsearch',     '~> 1.0.14'
+  s.add_runtime_dependency 'elasticsearch',     '>= 1.0.14', '< 6.2.0'
   s.add_runtime_dependency 'rest-client', '1.8.0'
   s.add_runtime_dependency 'sensu-plugin', '~> 1.2'