Upgrade rust/crates/protobuf-codegen to 2.18.1

Test: make
Change-Id: Ie57d9bfed5c5a2e142990d67ee5a2a9079351c8e
diff --git a/METADATA b/METADATA
index b44593d..a3beffb 100644
--- a/METADATA
+++ b/METADATA
@@ -7,13 +7,13 @@
   }
   url {
     type: ARCHIVE
-    value: "https://static.crates.io/crates/protobuf-codegen/protobuf-codegen-2.18.0.crate"
+    value: "https://static.crates.io/crates/protobuf-codegen/protobuf-codegen-2.18.1.crate"
   }
-  version: "2.18.0"
+  version: "2.18.1"
   license_type: NOTICE
   last_upgrade_date {
     year: 2020
-    month: 10
-    day: 6
+    month: 11
+    day: 24
   }
 }