Files.app: Fix date string generation for cloud import destinations.

BUG=451934

Review URL: https://codereview.chromium.org/879913005

Cr-Commit-Position: refs/heads/master@{#313666}

ui/file_manager/file_manager/background/js/media_import_handler.js

@@ -513,7 +513,7 @@ importer.MediaImportHandler.defaultDestination.getOrCreateImportDestination_ =
     var date = new Date();
     var year = date.getFullYear().toString();
     // Months are 0-based, but days aren't.
-    var month = padAndConvert(date.getMonth()) + 1;
+    var month = padAndConvert(date.getMonth() + 1);
     var day = padAndConvert(date.getDate());
 
     return year + '-' + month + '-' + day;