No module named 'apex' in colab notebook 00_NeMo_Primer.ipynb
**Describe the bug**

When running `00_NeMo_Primer.ipynb` notebook during `import nemo.collections.nlp as nemo_nlp` raises an error:
`ModuleNotFoundError: No module named 'apex'`

**Steps/Code to reproduce bug**

Opened in colab tutorial notebook [![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/NVIDIA/NeMo/blob/main/tutorials/00_NeMo_Primer.ipynb) and "Run all cells". Then after installation section at importing stage error raises.


**Expected behavior**

End-to-end notebook executions without errors.

**Environment overview (please complete the following information)**

 - Environment location: colab
 - Method of NeMo install: as in notebook
 ```
BRANCH = 'main'
!python -m pip install git+https://github.com/NVIDIA/NeMo.git@$BRANCH#egg=nemo_toolkit[all]
```

**Environment details**
- OS version: linux
- PyTorch version: 1.10.0+cu111
- Python version: 3.7.12

**Additional context**
Error occurs in both kernel-types: CPU and GPU.
![apex1](https://user-images.githubusercontent.com/36787333/151659365-9b5a7593-a343-4a8f-8f41-83ff04dfcfc4.jpg)
![apex2](https://user-images.githubusercontent.com/36787333/151659369-7af2fed5-83e7-4ff6-8917-d1960f473453.jpg)

