Update dependency to explicitly support version 7

Dependency has been updated to follow Elasticsearch gems' version policy.
This improves gem consistency and maintenance efficiency.

Author: aeroastro

elasticsearch-model/elasticsearch-model.gemspec

@@ -42,7 +42,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = '>= 2.4'
 
   s.add_dependency 'activesupport', '> 3'
-  s.add_dependency 'elasticsearch', '> 1'
+  s.add_dependency 'elasticsearch', '~> 7'
   s.add_dependency 'hashie'
 
   s.add_development_dependency 'activemodel', '> 3'