Make Operation generic

From https://github.com/anacrolix/stm/commit/80e033aa1f2218b83fb5891671ed795de72e19d5

1 files changed, 1 insertions, 1 deletions

diff --git a/tx.go b/tx.go
index 0d69498..2020308 100644
--- a/tx.go
+++ b/tx.go
@@ -114,7 +114,7 @@ type txProfileValue struct {
 
 // Retry aborts the transaction and retries it when a Var changes. You can return from this method
 // to satisfy return values, but it should never actually return anything as it panics internally.
-func (tx *Tx) Retry() interface{} {
+func (tx *Tx) Retry() struct{} {
 	retries.Add(txProfileValue{tx, tx.numRetryValues}, 1)
 	tx.numRetryValues++
 	panic(retry)