Update license.rtf to only have major version

[SteveL-MSFT]

PR Summary

Guidance is that we can just have the major version at the top "PowerShell 6" and not worry about updating the minor version with each release. The change is on line 230. Word made the other changes to the RTF.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.
• User-facing changes
  • Not Applicable
  • OR
  • User-facing Documentation needed
    • Issue filed - Issue link:
• Testing - New and feature
  • Not Applicable or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
    • Add [feature] if the change is significant or affects feature tests

[iSazonov]

Why the file in RTF format? It is not readable in browser. Make sense to convert it to simple text (Utf-8)?

[SteveL-MSFT]

@iSazonov this file is only shown in the MSI installer which requires RTF format

[anmenaga]

Fixed typo in PR title: "license.tf" -> "license.rtf"