Fix typo in first install command.

Remove `'` from `pip install nemo_toolkit[all]` as it caused the command to fail.

README.md

@@ -165,7 +165,7 @@ See the [model architecture](#model-architecture) section and [NeMo documentatio
 
 To train, fine-tune or play with the model you will need to install [NVIDIA NeMo](https://github.com/NVIDIA/NeMo). We recommend you install it after you've installed latest Pytorch version.
 ```
-pip install nemo_toolkit['all']
+pip install nemo_toolkit[all]
 ``` 
 
 ## How to Use this Model