prepare release v1.18.7

prepare release v1.18.6

prepare release v1.18.6.post0

Added scaling_type to Integer and Continuous ranges (aws#697)

Bump version to 1.18.4 (aws#687)

Fix README for PyPI (aws#643)

Bump version to v1.18.3 (aws#641)

Bump version to 1.18.2 (aws#615)

Bump version to 1.18.1 (aws#611)

Bumping up version to 1.18.0 for horovod release (aws#604)

* Bumping up version to 1.18.0 for horovod release