Doesn't validate number of files when is not multiple

[RezaRahmati]

Steps to reproduce

1 - Open the demo page
2 - Drag 2 files to "Base Drop Zone" area

Expected Behavior:
Zone become Red, since it doesn't accept multiple

Actual Behavior:
Zone become Green

[AckerApple]

Will most likely need a pull request for this.

[RezaRahmati]

@AckerApple Hi Acker, is there any plan to fix this?