[omaha-client] Small fix for rust doc.

Use //! instead of /// for crate/module level doc.

Test: fx rustdoc garnet/lib/rust/omaha_client --open
Change-Id: I4b62b841e37d5bb588393e3381419e6a7a99cb59
diff --git a/garnet/lib/rust/omaha_client/src/common/mod.rs b/garnet/lib/rust/omaha_client/src/common/mod.rs
index a230143..3da791b 100644
--- a/garnet/lib/rust/omaha_client/src/common/mod.rs
+++ b/garnet/lib/rust/omaha_client/src/common/mod.rs
@@ -2,13 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+//! The omaha_client::common module contains those types that are common to many parts of the
+//! library.  Many of these don't belong to a specific sub-module.
+
 use crate::protocol::request::InstallSource;
 use std::fmt;
 use std::time::SystemTime;
 
-/// The omaha_client::common module contains those types that are common to many parts of the
-/// library.  Many of these don't belong to a specific sub-module.
-
 /// Omaha has historically supported multiple methods of counting devices.  Currently, the
 /// only recommended method is the Client Regulated - Date method.
 ///
diff --git a/garnet/lib/rust/omaha_client/src/lib.rs b/garnet/lib/rust/omaha_client/src/lib.rs
index ba0b047..b0de90d 100644
--- a/garnet/lib/rust/omaha_client/src/lib.rs
+++ b/garnet/lib/rust/omaha_client/src/lib.rs
@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-//! Crate omaha_client
 //! This is for Omaha client binaries written in Rust.
 
 #![feature(async_await, await_macro, futures_api)]