Fixed Vulnerability details for GHSA-wrxf-x8rm-6ggg

Before:

* fluentd and fluentd-ui was marked as vulnerable
* It mentions https://github.com/fluent/fluentd/issues/2722 in
`GHSA-wrxf-x8rm-6ggg` References.

After:

* Only fluentd-ui should be marked as vulnerable
* In `GHSA-wrxf-x8rm-6ggg` References were updated from
https://github.com/fluent/fluentd/issues/2722
to fluent/fluentd-ui#295.

Thus, gems/fluentd/CVE-2020-21514.yml is inappropriate now and
should be removed.
Also, reference url in gems/fluentd-ui/CVE-2020-21514.yml should be
updated.

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

Author: kenhys

gems/fluentd-ui/CVE-2020-21514.yml

@@ -14,5 +14,5 @@ notes: Never patched
 related:
   url:
     - https://nvd.nist.gov/vuln/detail/CVE-2020-21514
-    - https://github.com/fluent/fluentd/issues/2722
+    - https://github.com/fluent/fluentd-ui/issues/295
     - https://github.com/advisories/GHSA-wrxf-x8rm-6ggg