Adjusted the TLS12 method based on discussions in Slack Chat

Description

As per PowerShell Slack conversation, improve the TLS1.2 implementation

Related Issue

Motivation and Context

TLS Support in SLACK is deprecated for anything less than 1.2, which resulted in a conversation around TLS1.2 implementation in the PowerShell slack channel for ChatOps, which resulted in this suggested change

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[x ] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[x ] I have read the CONTRIBUTING document.
[ ] I have added tests to cover my changes.
[ ] All new and existing tests passed.

poshbotio / PoshBot

Adjusted the TLS12 method based on discussions in Slack Chat #204