imports cleanup

src/pocketmine/scheduler/AsyncTask.php

@@ -27,6 +27,7 @@ use pocketmine\Collectable;
 use pocketmine\Server;
 use pocketmine\utils\AssumptionFailedError;
 use function is_scalar;
+use function is_string;
 use function serialize;
 use function unserialize;
 

src/pocketmine/scheduler/SendUsageTask.php

@@ -34,6 +34,7 @@ use pocketmine\utils\VersionString;
 use function array_values;
 use function count;
 use function json_encode;
+use function json_last_error_msg;
 use function md5;
 use function microtime;
 use function php_uname;