Make UnabortableTransactionError Copy

Author: spacejam

src/transaction.rs

@@ -99,7 +99,7 @@ pub struct TransactionalTree {
 
 /// An error type that is returned from the closure
 /// passed to the `transaction` method.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum UnabortableTransactionError {
     /// An internal conflict has occurred and the `transaction` method will
     /// retry the passed-in closure until it succeeds. This should never be