upgrade to Serialport 8

[noopkat]

Description

This lib badly needs an upgrade to serialport v8 in order to stay compatible with new and current versions of NodeJS.

Type of change

Please delete options that are not relevant.

• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] This change requires a documentation update

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules
• [x] Changes have been manually tested (please provide information on test platform using the fields below)

Test / Development Platform Information

• Operating system and version: macOS High Sierra and Windows 10
• Avrgirl Arduino version
• NodeJS version: v8, v10, v12
• Arduino Board being used: Uno, Mega, and Micro

[coveralls]

Coverage decreased (-0.1%) to 44.404% when pulling d82eeed62e6fa4f46418416fb10b4adff162be0a on serialport8 into 1dfd9c12f12a3076ad131199952e23543f15e9fd on master.

[noopkat]

this is going to be a major version bump due to removing support for older NodeJS versions.