Private Space documentation updated to state that inter-region peering is possible

Change effective on 06 March 2018

Previously the Private Space Peering documentation stated that peering Heroku Private Spaces with AWS VPCs in regions other than the private space region was not supported.

This documentation has been changed to state that inter-region peering is supported with the caveats called out in AWS VPC docs. No Heroku product changes were introduced.