fix markdown (#4265)

Author: AlekseySh

docs/tutorials/customize_runtime.md

@@ -180,7 +180,7 @@ so that 1 epoch for training and 1 epoch for validation will be run iteratively.
 
 1. The parameters of model will not be updated during val epoch.
 2. Keyword `total_epochs` in the config only controls the number of training epochs and will not affect the validation workflow.
-3. Workflows `[('train', 1), ('val', 1)]` and `[('train', 1)]` will not change the behavior of `EvalHook` because `EvalHook` is called by `after_train_epoch` and validation workflow only affect hooks that are called through `after_val_epoch`. Therefore, the only difference between `[('train', 1), ('val', 1)]` and ``[('train', 1)]` is that the runner will calculate losses on validation set after each training epoch.
+3. Workflows `[('train', 1), ('val', 1)]` and `[('train', 1)]` will not change the behavior of `EvalHook` because `EvalHook` is called by `after_train_epoch` and validation workflow only affect hooks that are called through `after_val_epoch`. Therefore, the only difference between `[('train', 1), ('val', 1)]` and `[('train', 1)]` is that the runner will calculate losses on validation set after each training epoch.
 
 ## Customize hooks