s/an map/a map/

Author: apasel422

index.bs

@@ -2456,7 +2456,7 @@ To <dfn>parse aggregation keys</dfn> given a [=map=] |map|:
 1. Let |aggregationKeys| be a new [=map=].
 1. If |map|["<code>[=source-registration JSON key/aggregation_keys=]</code>"] does not [=map/exist=], return |aggregationKeys|.
 1. Let |values| be |map|["<code>[=source-registration JSON key/aggregation_keys=]</code>"].
-1. If |values| is not an [=map=], return an error.
+1. If |values| is not a [=map=], return an error.
 1. If |values|'s [=map/size=] is greater than the
     [=max aggregation keys per source registration=], return an error.
 1. [=map/iterate|For each=] |key| → |value| of |values|: