Bump the CACHE_COMMONMARK_VERSION

to ensure any markdown generated before the asset
proxy default was corrected is re-generated

changelogs/unreleased/bw-asset-proxy-markdown-bump.yml

+---
+title: Bump markdown cache version to fix any incorrect links from asset proxy defaults
+merge_request:
+author:
+type: fixed

lib/gitlab/markdown_cache.rb

@@ -3,7 +3,7 @@
 module Gitlab
   module MarkdownCache
     # Increment this number every time the renderer changes its output
-    CACHE_COMMONMARK_VERSION        = 17
+    CACHE_COMMONMARK_VERSION        = 18
     CACHE_COMMONMARK_VERSION_START  = 10
     BaseError = Class.new(StandardError)