DEP: add botocore to install_requires

[snowman2]

Missing in install requires:

aws-requests-auth/setup.py

Line 13 in 2e1dd0f

install_requires=['requests>=0.14.0'],

Used in code here

aws-requests-auth/aws_requests_auth/boto_utils.py

Line 7 in 2e1dd0f

from botocore.session import Session