Typo in TrOCR documentation
decoder_layerdrop was hidden in [TrOCR documentation](https://huggingface.co/docs/transformers/v4.21.1/en/model_doc/trocr#transformers.TrOCRConfig). 😂

![image](https://user-images.githubusercontent.com/61103343/185959294-741f0f0d-999f-4073-a4b1-7ee7d5be2184.png)

I think it should be revised as follows.


- **init_std** (float, optional, defaults to 0.02) — The standard deviation of the truncated_normal_initializer for initializing all weight matrices.
- **decoder_layerdrop** — (float, optional, defaults to 0.0): The LayerDrop probability for the decoder. See the [LayerDrop paper](see https://arxiv.org/abs/1909.11556) for more details.
I found typo in TrOCRConfig docstring~

https://github.com/huggingface/transformers/blob/84beb8a49bf137a88d1b29ab3a85ba0a3cd097d5/src/transformers/models/trocr/configuration_trocr.py#L70

It revised as follows. (remove ':' ) #18721 

```python
decoder_layerdrop (`float`, *optional*, defaults to 0.0):
```