Fix typo in docstring (#5835)

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pytorch_lightning/plugins/apex.py

@@ -104,11 +104,12 @@ class ApexPlugin(PrecisionPlugin):
         """
         This code is a modification of :meth:`torch.nn.utils.clip_grad_norm_` using a higher epsilon for fp16 weights.
         This is important when setting amp_level to O2, and the master weights are in fp16.
+
         Args:
             grad_clip_val: Maximum norm of gradients.
             optimizer: Optimizer with gradients that will be clipped.
             norm_type: (float or int): type of the used p-norm. Can be ``'inf'`` for
-            infinity norm.
+                infinity norm.
         """
         model = self.trainer.get_model()
         parameters = model.parameters()