Add edenchuang as payment-request/ reviewer (#13440)

Repeats https://github.com/web-platform-tests/wpt/pull/12352 against the
master branch.
diff --git a/payment-request/META.yml b/payment-request/META.yml
index f8460d4..0a075e1 100644
--- a/payment-request/META.yml
+++ b/payment-request/META.yml
@@ -6,3 +6,4 @@
   - MSFTkihans
   - mnoorenberghe
   - romandev
+  - edenchuang