Make OAuthUserStore Sync and Send
Require that implementations of the OAuthUserStore trait are Sync and
Send.  This will facilitate the use of the store with REST resources.
@@ -226,7 +226,7 @@ impl OAuthUserUpdateBuilder {
}
/// Defines methods for CRUD operations and fetching OAuth user information.
-pub trait OAuthUserStore {
+pub trait OAuthUserStore: Send + Sync {
/// Add an OAuthUser to the store.
///
/// # Errors
