config: end the file with a newline

Small cosmetic change, POSIX requires final newlines in text files.

https://stackoverflow.com/questions/729692/why-should-text-files-end-with-a-newline

app/server/lib/config.ts

@@ -98,7 +98,7 @@ export class FileConfig<FileContents> {
   }
 
   public async persistToDisk() {
-    await Deps.writeFile(this._filePath, JSON.stringify(this._rawConfig, null, 2));
+    await Deps.writeFile(this._filePath, JSON.stringify(this._rawConfig, null, 2) + "\n");
   }
 }