Fix markdown rendering of Connection::transaction doc
This fixes `DropBehavior::Commit` being rendered as `DropBehavior: :Commit`.
@@ -378,8 +378,8 @@ impl Connection {
///
/// The transaction defaults to rolling back when it is dropped. If you
/// want the transaction to commit, you must call
- /// [`commit`](Transaction::commit) or [`set_drop_behavior(DropBehavior:
- /// :Commit)`](Transaction::set_drop_behavior).
+ /// [`commit`](Transaction::commit) or
+ /// [`set_drop_behavior(DropBehavior::Commit)`](Transaction::set_drop_behavior).
///
/// ## Example
///
