Fix Docs and system checks for Elasticsearch version compatibility

doc/integration/elasticsearch.md

@@ -19,7 +19,8 @@ special searches:
 | -------------- | --------------------- |
 | GitLab Enterprise Edition 8.4 - 8.17   | Elasticsearch 2.4 with [Delete By Query Plugin](https://www.elastic.co/guide/en/elasticsearch/plugins/2.4/plugins-delete-by-query.html) installed |
 | GitLab Enterprise Edition 9.0 - 11.4   | Elasticsearch 5.1 - 5.5 |
-| GitLab Enterprise Edition 11.5+        | Elasticsearch 5.6 - 6.x |
+| GitLab Enterprise Edition 11.5 - 12.6  | Elasticsearch 5.6 - 6.x |
+| GitLab Enterprise Edition 12.7+        | Elasticsearch 6.x - 7.x |
 
 ## Installing Elasticsearch
 

ee/lib/system_check/app/elasticsearch_check.rb

@@ -21,10 +21,10 @@ module SystemCheck
 
       def check?
         case self.class.current_version.major
-        when 5
-          !(1..5).cover?(self.class.current_version.minor)
         when 6
           true
+        when 7
+          true
         else
           false
         end

ee/spec/lib/system_check/app/elasticsearch_check_spec.rb

@@ -32,11 +32,12 @@ describe SystemCheck::App::ElasticsearchCheck do
     where(:version, :result) do
       '2.3.0' | false
       '5.3.1' | false
-      '5.6.0' | true
-      '5.6.6' | true
+      '5.6.0' | false
+      '5.6.6' | false
       '6.0.0' | true
-      '6.3.4' | true
-      '7.1.0' | false
+      '6.4.2' | true
+      '7.1.0' | true
+      '7.5.1' | true
     end
 
     with_them do