fix pep8 issues

Author: kaushikb11

pytorch_lightning/trainer/training_loop.py

@@ -296,7 +296,7 @@ def training_step(self, split_batch, batch_idx, opt_idx, hiddens):
             self.trainer.logger_connector.cache_logged_metrics()
 
             self._check_training_step_output(training_step_output)
-            
+
             training_step_output = self.trainer.call_hook("training_step_end", training_step_output)
 
             training_step_output_for_epoch_end, training_step_output = self._process_training_step_output(