data/reports: add vulnerable_at to GO-2021-0113.yaml

Aliases: CVE-2021-38561, GHSA-ppp9-7jff-5vj2

Updates golang/vulndb#113

Change-Id: I1b6108e968286216b1e353987e59da0fb9c0acc5
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/465180
Reviewed-by: Tim King <taking@google.com>
Run-TryBot: Tatiana Bradley <tatianabradley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

data/reports/GO-2021-0113.yaml

@@ -2,6 +2,7 @@ modules:
   - module: golang.org/x/text
     versions:
       - fixed: 0.3.7
+    vulnerable_at: 0.3.6
     packages:
       - package: golang.org/x/text/language
         symbols:
@@ -10,7 +11,6 @@ modules:
           - MatchStrings
           - MustParse
           - ParseAcceptLanguage
-        skip_fix: 'TODO: fill this out [or set vulnerable_at to derive symbols]'
 description: |
     Due to improper index calculation, an incorrectly formatted language tag can cause Parse
     to panic via an out of bounds read. If Parse is used to process untrusted user inputs,