6.8.20 version bump (#2244)

Updates version for the 6.8.20 release

DO NOT MERGE UNTIL RELEASE DAY

Author: KOTungseth

shared/versions/stack/6.8.asciidoc

@@ -1,12 +1,12 @@
-:version:                6.8.19
+:version:                6.8.20
 ////
 bare_version never includes -alpha or -beta
 ////
-:bare_version:           6.8.19
-:logstash_version:       6.8.19
-:elasticsearch_version:  6.8.19
-:kibana_version:         6.8.19
-:apm_server_version:     6.8.19
+:bare_version:           6.8.20
+:logstash_version:       6.8.20
+:elasticsearch_version:  6.8.20
+:kibana_version:         6.8.20
+:apm_server_version:     6.8.20
 :branch:                 6.8
 :minor-version:          6.8
 :major-version:          6.x