Update docs for version 2 of MobileNet V2

[danhamill]

Apparently, version 1 of mobilenet v2 has been replaced updated to version 2. Version 1 wasn't responsive to fine-tuning.

Replace:

https://tfhub.dev/google/imagenet/mobilenet_v2_100_96/classification/1

with:

https://tfhub.dev/google/imagenet/mobilenet_v2_100_96/classification/2