No matching distribution found for matplotlib==3.1.2 (from -r requirements.txt (line 5))

Hi, I was trying to setup the environment to use the examples in this book. I am using Ubuntu 16.04.

When I tried the following command,
```
(env) paean@paean-ws:~/devel/handson-ml$ python3 -m pip install --upgrade -r requirements.txt
```

I got the following error message.
```
Collecting jupyter==1.0.0
Using cached https://files.pythonhosted.org/packages/83/df/0f5dd132200728a86190397e1ea87cd76244e42d39ec5e88efd25b2abd7e/jupyter-1.0.0-py2.py3-none-any.whl
ERROR: Could not find a version that satisfies the requirement matplotlib==3.1.2 (from -r requirements.txt (line 5)) (from versions: 0.86, 0.86.1, 0.86.2, 0.91.0, 0.91.1, 1.0.1, 1.1.0, 1.1.1, 1.2.0, 1.2.1, 1.3.0, 1.3.1, 1.4.0, 1.4.1rc1, 1.4.1, 1.4.2, 1.4.3, 1.5.0, 1.5.1, 1.5.2, 1.5.3, 2.0.0b1, 2.0.0b2, 2.0.0b3, 2.0.0b4, 2.0.0rc1, 2.0.0rc2, 2.0.0, 2.0.1, 2.0.2, 2.1.0rc1, 2.1.0, 2.1.1, 2.1.2, 2.2.0rc1, 2.2.0, 2.2.2, 2.2.3, 2.2.4, 3.0.0rc2, 3.0.0, 3.0.1, 3.0.2, 3.0.3)
ERROR: No matching distribution found for matplotlib==3.1.2 (from -r requirements.txt (line 5))
```

Anyone saw this before and any suggestions how to overcome it? I am not particular familiar with the pip and how it works.

Thanks.