add default command to the download and install task so that VS Code does not complains on linux

.vscode/tasks.json

@@ -12,6 +12,7 @@
         {
             "label": "Download and install the windows dependencies (Windows10)",
             "type": "shell",
+            "command": "echo 'nothing to do'",
             "windows": {
                 "command": [
                     "if (Test-Path -Path 'C:\\sextant') {rmdir -r C:\\sextant};",