Auto-create data dir when updating lib indexes

Author: cmaglie

Diff for: arduino/libraries/librariesmanager/download.go

@@ -28,6 +28,7 @@ var LibraryIndexURL, _ = url.Parse("https://downloads.arduino.cc/libraries/libra
 
 // UpdateIndex downloads the libraries index file from Arduino repository.
 func (lm *LibrariesManager) UpdateIndex() (*downloader.Downloader, error) {
+	lm.IndexFile.Parent().MkdirAll()
 	lm.IndexFile.Remove()
 	// TODO: Download from gzipped URL index
 	return downloader.Download(lm.IndexFile.String(), LibraryIndexURL.String())