Replace "user agent" by "application" in readOnly description

The term "user agent" is appropriate in the scope of hypermedia,
not that much elsewhere; "application" is more generic.

Author: dlax

jsonschema-validation.xml

@@ -746,8 +746,8 @@
                 </t>
                 <t>
                     If it has a value of boolean true, this keyword indicates that the value of the
-                    instance is managed exclusively by the owning authority, and attempts by a user
-                    agent to modify the value of this property are expected to be ignored or
+                    instance is managed exclusively by the owning authority, and attempts by an
+                    application to modify the value of this property are expected to be ignored or
                     rejected by that owning authority.
                 </t>
                 <t>