Changed returntype of Database::transaction to mixed to reflect that the return of a transaction is returned by this function-call

Author: rkrx

src/Database.php

@@ -101,7 +101,7 @@ public function transactionRollback();
 	/**
 	 * @param int|callable $tries
 	 * @param callable|null $callback
-	 * @return $this
+	 * @return mixed
 	 * @throws \Exception
 	 */
 	public function transaction($tries = 1, $callback = null);

src/Databases/MySQL.php

@@ -238,7 +238,7 @@ public function transactionRollback() {
 	/**
 	 * @param int|callable $tries
 	 * @param callable|null $callback
-	 * @return $this
+	 * @return mixed
 	 * @throws \Exception
 	 */
 	public function transaction($tries = 1, $callback = null) {