Playback error - missing Widevine libraries

*I'm submitting a ...*
- [x ] bug report
- [ ] feature request
- [ ] support request

## General information

### Prerequisites

* [Y ] Are you running the latest version?

### Description

The Netflix add-on starts up ok and I can see menus of content, but when I try to play an item I get the following error:

Your system is missing the following libraries required by Widevine CDM: libnss3.so, libnssutil3.so, libnspr4.so. Install the libraries to play this content.

### Steps to Reproduce

1. [First Step]
2. [Second Step]
3. [and so on...]

**Expected behavior:** [What you expected to happen]

**Actual behavior:** [What actually happened]

## Context (Environment)

### Installation

* [x ] I installed the plugin via zip from the Releases page
* [ ] I´m using the Netflix Repo
* [ ] I´m using a different source (Please tell which)

### Operating System

* [x ] Linux (x86/x64)
* [ ] OSX (x86/x64)
* [ ] Windows (x86/x64)
* [ ] Linux (ARM)
* [ ] Android

#### Additional information on the environment

Running Retropie 4.4, updated Kodi to v18 via an unstable repo.

Kodi 18.0-BETA3 Git:20180911-83d2d3c5d0-dirty

Installed Python 2 and PIP to get Cryptodomex loaded.

Installed the add-on yesterday (28-Sep) for the first time, have never tried installing it in the past.

Allowed the Netflix add-on to install the Widevine library automatically.

## Debug log

https://drive.google.com/file/d/1_qxn1KFu5NQ8kVhIhxmk7ds4QNqMLoMv/view?usp=sharing

## Other information

[e.g. detailed explanation, related issues, suggestions how to fix, links for us to have context, etc.]

### Screenshots

[Please add a screenshot if that helps understanding your problem]

[You can erase any parts of this template not applicable to your Issue.]

The report names no source file, test, or entry point. Start by reviewing the linked debug log and reproducing on RetroPie with Kodi 18 and the listed Linux libraries, then inspect the add-on's Widevine setup behavior. Done means playback works with the required dependencies or the supported environment and dependency requirements are clearly established.

Written by the indexing model from the issue text.