Upgrade rust/crates/protobuf-codegen to 2.18.1

Test: make
Change-Id: Ie57d9bfed5c5a2e142990d67ee5a2a9079351c8e
diff --git a/src/lib.rs b/src/lib.rs
index 8e519d4..8011bc1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -192,7 +192,7 @@
     {
         let mut w = CodeWriter::new(&mut v);
 
-        w.write_generated_by("rust-protobuf", "2.18.0");
+        w.write_generated_by("rust-protobuf", "2.18.1");
         w.write_line(&format!("//! Generated file from `{}`", file.get_name()));
         if customize.inside_protobuf != Some(true) {
             w.write_line("");