[STORE] Update the elasticsearch-model dependency in gemspec

Author: estolfo

elasticsearch-persistence/elasticsearch-persistence.gemspec

@@ -23,8 +23,8 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = ">= 1.9.3"
 
-  s.add_dependency "elasticsearch",       '~> 5'
-  s.add_dependency "elasticsearch-model", '~> 5'
+  s.add_dependency "elasticsearch",       '~> 6'
+  s.add_dependency "elasticsearch-model", '~> 6'
   s.add_dependency "activesupport",       '> 4'
   s.add_dependency "activemodel",         '> 4'
   s.add_dependency "hashie"