Made migration binary use tokio instead of async-std to reduce the amount of dependencies

migration/src/main.rs

@@ -1,6 +1,6 @@
 use sea_orm_migration::prelude::*;
 
-#[async_std::main]
+#[tokio::main(flavor = "current_thread")]
 async fn main() {
     cli::run_cli(migration::Migrator).await;
 }