chore: update license text to fix GitHub license recognition

[ericrallen]

The current, incorrect format of the LICENSE file prevents GitHub from recognizing the license type which leads to the GitHub API response giving a response without any relevant license info and prevents the GitHub web interface from displaying any license details and information.

The issue can be solved by just putting MIT License at the top of the file instead of SatchelJS, but it also seemed prudent to update the formatting to match the standard MIT license included in most projects and follow the format of the MIT License LICENSE file from other Microsoft projects.

I took the license text in this PR from the VS Code project's LICENSE.txt file, and updated the copyright date to match the year of the first commit in this repo.

Here is the GitHub API response for basic license information from microsoft/satcheljs:

{
  "data": {
    "repository": {
      "nameWithOwner": "microsoft/satcheljs",
      "licenseInfo": {
        "name": "Other",
        "spdxId": "NOASSERTION",
        "pseudoLicense": true,
        "hidden": true,
        "featured": false,
        "url": "http://choosealicense.com/licenses/other/",
        "description": null
      }
    }
  }
}

And here is the response for basic license information for microsoft/vscode:

{
  "data": {
    "repository": {
      "nameWithOwner": "microsoft/vscode",
      "licenseInfo": {
        "name": "MIT License",
        "spdxId": "MIT",
        "pseudoLicense": false,
        "hidden": false,
        "featured": true,
        "url": "http://choosealicense.com/licenses/mit/",
        "description": "A short and simple permissive license with conditions only requiring preservation of copyright and license notices. Licensed works, modifications, and larger works may be distributed under different terms and without source code."
      }
    }
  }
}

You can see an example of the extended License information that GitHub shows in it's web interface by looking at the LICENSE.txt file for VS Code and in the included screenshot below.