doc: fix example commands for REPLACEME updates

Split the two example command lines for updating the `REPLACEME` tags
into separate `console` fenced code blocks. This fixes some stray
"`" characters and makes each example one-click copiable when viewing
the guide in GitHub's web UI.

doc/guides/releases.md

@@ -326,7 +326,11 @@ grep REPLACEME doc/api/*.md
 and substitute this node version with
 
 ```console
-sed -i "s/REPLACEME/$VERSION/g" doc/api/*.md` or `perl -pi -e "s/REPLACEME/$VERSION/g" doc/api/*.md
+sed -i "s/REPLACEME/$VERSION/g" doc/api/*.md
+```
+or
+```console
+perl -pi -e "s/REPLACEME/$VERSION/g" doc/api/*.md
 ```
 
 `$VERSION` should be prefixed with a `v`.