fix(server): Adding logger import to t5_modeling.py (#585)

Logger is referenced during the apex importing but is not imported,
causing a NameError

server/text_generation_server/models/custom_modeling/t5_modeling.py

@@ -19,6 +19,8 @@ import math
 import warnings
 from typing import Optional, Tuple, Union
 
+from loguru import logger
+
 import torch
 import torch.distributed
 from torch import nn