move hpa to the correct spot in the glossary (kubernetes-sigs#1047)

Author: tariq1890

docs/book/GLOSSARY.md

@@ -64,12 +64,12 @@ The set of Kubernetes services that form the basis of a cluster. See also https:
 
 A feature implementation offered as part of the Cluster API project, infrastructure providers can swap it out for a different one.
 
+# H
+
 ## Horizontal Scaling
 
 The ability to add more machines based on policy and well defined metrics. For example, add a machine to a cluster when CPU load average > (X) for a period of time (Y).
 
-# H
-
 ## Host
 
 see [Server](#server)