Update typo which gives issue for pytorch 1.3.1 (#103)

* Update typo which gives issue for pytorch 1.3.1

On lassen we use 1.3.1 which showed this bug.

* persistent workers do not exist in 1.3.1

dlio_benchmark/data_loader/torch_data_loader.py

@@ -96,10 +96,11 @@ def read(self):
             kwargs={}
         else:
             kwargs={'multiprocessing_context':self._args.multiprocessing_context,
-                    'prefetch_factor': prefetch_factor, 
-                    'persistent_workers': True}
+                    'prefetch_factor': prefetch_factor}
+            if torch.__version__ != '1.3.1':       
+                kwargs['persistent_workers'] = True
         if torch.__version__ == '1.3.1':
-            if 'prefetch_factor' in kargs:
+            if 'prefetch_factor' in kwargs:
                 del kwargs['prefetch_factor']
             self._dataset = DataLoader(dataset,
                                        batch_size=self.batch_size,