message: Update extension version for 1.15.0-beta6 and fix deprecated category
diff: {
  "name": "csharp",
  "publisher": "ms-vscode",
  - "version": "1.15.0-beta5",
  + "version": "1.15.0-beta6",
  "description": "C# for Visual Studio Code (powered by OmniSharp).",
  "displayName": "C#",
  "author": "Microsoft Corporation",
  },
  "categories": [
  "Debuggers",
  - "Languages",
  + "Programming Languages",
  "Linters",
  "Snippets"
  ],
  