Wrong image preprocessing

[WeidiXie]

Hi,

Thank you very much for providing this keras version code.

Just want to mention, I think the image processing is wrong in your code.

Directly resizing to 224 may lead problem, which can degrade the performance, because the aspect ratio of the face has been changed.

Best

[rcmalli]

This is true but users are free to use their own preprocessing scaling steps with this library