[runtimes/rust] Fix link to serde_json5 mirror

Change-Id: Ifeaedb5edac9c7a7c94d2cd14157e21a362f6c92
Reviewed-on: https://fuchsia-review.googlesource.com/c/manifest/+/410755
Reviewed-by: Tyler Mandry <tmandry@google.com>
diff --git a/runtimes/rust b/runtimes/rust
index 09cd2df..f6c397e 100644
--- a/runtimes/rust
+++ b/runtimes/rust
@@ -36,7 +36,7 @@
              historydepth="1"/>
     <project name="third_party/serde_json5"
              path="third_party/rust-mirrors/serde_json5"
-             remote="https://fuchsia.googlesource.com/third_party/serde_json5"
+             remote="https://fuchsia.googlesource.com/third_party/github.com/google/serde_json5"
              gerrithost="https://fuchsia-review.googlesource.com"
              githooks="manifest/git-hooks"/>
     <project name="third_party/tokio-core"