Update collection-spec/collection-spec.md

Co-authored-by: Phil Varner <[email protected]>

Author: matthewhanson

collection-spec/collection-spec.md

@@ -69,7 +69,7 @@ A list of extensions the Collection implements.
 The list consists of URLs to JSON Schema files that can be used for validation.
 This list must only contain extensions that extend the Collection specification itself,
 see the the 'Scope' for each of the extensions.
-This must **not** declare the extensions that are only implemented in child Collection or Items.
+This must **not** declare the extensions that are only implemented in child Collection objects or child Item objects.
 
 #### id