[roll third_party/pigweed] docs: Update changelog

Original-Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/191271

https://pigweed.googlesource.com/pigweed/pigweed
third_party/pigweed Rolled-Commits: 13eacb6f3f68647..ca188a7fd5829b2
Roller-URL: https://ci.chromium.org/b/8756534724203357233
GitWatcher: ignore
CQ-Do-Not-Cancel-Tryjobs: true
Change-Id: I78ba0d8a8d40ff47acf17231c92ec3ccb30215d3
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/experimental/+/191330
Bot-Commit: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
Commit-Queue: Pigweed Roller <pigweed-roller@pigweed-service-accounts.iam.gserviceaccount.com>
diff --git a/third_party/pigweed b/third_party/pigweed
index 13eacb6..ca188a7 160000
--- a/third_party/pigweed
+++ b/third_party/pigweed
@@ -1 +1 @@
-Subproject commit 13eacb6f3f68647d094db04ae3ce1db856d21bb6
+Subproject commit ca188a7fd5829b25b306bdf35b888ce8049a2b7c