changed HA backup to HA replica

@nathos had a great recommendation to not use the term HA backup as it confuses things and instead use HA replica. I think he was spot on and made the changes.

Author: Matt Duff

README.md

@@ -232,8 +232,9 @@ Note: the `GHE_DATA_DIR` variable set in `backup.config` can be used to change
 the disk location where snapshots are written.
 
 ### How does this data differ from the HA (High Availability) backup data?
-##### The purpose of the High Avaibility backup
-These two backups serve different purposes. The [HA backup](https://help.github.com/enterprise/2.0/admin-guide/high-availability-cluster-configuration/) has the primary purpose of being another a backup instance that is ready in case the primary instance becomes unavailable. The HA backup pulls data from the primary instance to ensure it is up to date in case it needs to be promoted to the primary instance. In that sense the HA backup has all the data and configuration of the primary instance. This data on the HA instance is not usable by other instances without being extracted by the backup-utils.
+
+##### The purpose of the High Avaibility replica
+These two tools serve different purposes. The [HA replica](https://help.github.com/enterprise/2.0/admin-guide/high-availability-cluster-configuration/) has the primary purpose of being another a replica instance that is ready in case the primary instance becomes unavailable. The HA replica pulls data from the primary instance to ensure it's data is current in the case it needs to be promoted to the primary instance. In that sense the HA replica has all the data and configuration of the primary instance. However, this data on the HA instance is not usable by other instances without being extracted by the backup-utils.
 
 ##### The purpose of the backup-utils
 The backup-utils data is meant to be used to restore an instance or set up a new instance. This backup data does not require the overhead of having a VM that can support running GitHub Enterprise. The backup-utils utility only copies over repository data, along with full snapshots of all other pertinent data stores. and formats this data so it can be reused in the restoration or setup of an instance.