Update the downloaded Python language server nuget package filename.

Fixes microsoft#2362

- Coincides with addition to CI/CD pipeline
- CI/CD pipeline copies the latest bits to a static file name
- We need to use a specific name.
- We want the bits to be updatable.
- Until we ship non-beta python language server this will work.

news/2 Fixes/2362.md

@@ -0,0 +1 @@
+Update the downloaded Python language server nuget package filename to 'Python-Language-Server-{OSType}.beta.nupkg'.

src/client/activation/downloader.ts

@@ -20,7 +20,7 @@ const StreamZip = require('node-stream-zip');
 
 const downloadUriPrefix = 'https://pvsc.blob.core.windows.net/python-language-server';
 const downloadBaseFileName = 'Python-Language-Server';
-const downloadVersion = '0.1.18204.3';
+const downloadVersion = 'beta';
 const downloadFileExtension = '.nupkg';
 
 export const DownloadLinks = {