Update links in sagemaker/image_uris.py

[NouamaneTazi]

This page is no longer available:

sagemaker-python-sdk/src/sagemaker/image_uris.py

Line 55 in 99f023e

https://aws.amazon.com/sagemaker/pricing/instance-types. This is required if

It should probably be replaced with:
https://aws.amazon.com/sagemaker/pricing/

[ahsan-z-khan]

Updated link