Docs: Fix :issue: and :pull: asciidoc replacements

Closes #14922

docs/reference/index.asciidoc

@@ -7,8 +7,8 @@
 :jdk:           1.8.0_25
 :defguide:      https://www.elastic.co/guide/en/elasticsearch/guide/current
 :plugins:       https://www.elastic.co/guide/en/elasticsearch/plugins/master
-:issue:         https://github.com/elastic/elasticsearch/issues
-:pull:          https://github.com/elastic/elasticsearch/pull
+:issue:         https://github.com/elastic/elasticsearch/issues/
+:pull:          https://github.com/elastic/elasticsearch/pull/
 
 include::getting-started.asciidoc[]