Fast fixes for compatibility with tensorflow 2.6

[DavidDoukhan]

Dear @rcmalli ,

Please find bellow a small contribution to update keras-vggface and make it compliant with current tensorflow 2.6. I use your package in one of my project which requires up-to-date version of tensorflow.

By the way, is there a way to cite your work when doing a publication ?

Kind regards,

[DavidDoukhan]

By the way, you can ignore commit 27a5bb1b5f5be568a780d0d7f9e53bdc78b763f6 This was done only allow me to package your work and use it easily in other projects