Minor Elasticsearch task description updates

[ci skip]

lib/tasks/gitlab/elastic.rake

 namespace :gitlab do
   namespace :elastic do
     desc "GitLab | Update Elasticsearch indexes"
-    task index: :environment do
+    task :index do
       Rake::Task["gitlab:elastic:index_repositories"].invoke
       Rake::Task["gitlab:elastic:index_wikis"].invoke
       Rake::Task["gitlab:elastic:index_database"].invoke
     end
 
-    desc "GitLab | Update Elasticsearch indexes for Repository"
+    desc "GitLab | Update Elasticsearch indexes for project repositories"
     task index_repositories: :environment  do
       Repository.__elasticsearch__.create_index!
 
@@ -54,7 +54,7 @@ namespace :gitlab do
       end
     end
 
-    desc "GitLab | Update Elasticsearch indexes for Wiki"
+    desc "GitLab | Update Elasticsearch indexes for wiki repositories"
     task index_wikis: :environment  do
       ProjectWiki.__elasticsearch__.create_index!