Fix typo in configuration metadata appendix

See spring-projectsgh-18289

Closes spring-projectsgh-18289

Author: AlexFalappa

spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-configuration-metadata.adoc

@@ -266,7 +266,7 @@ The JSON object contained in the `hints` array can contain the attributes shown
 | String
 | The full name of the property to which this hint refers.
   Names are in lower-case period-separated form (such as `spring.mvc.servlet.path`).
-  If the property refers to a map (such as `system.contexts`), the hint either applies to the _keys_ of the map (`system.context.keys`) or the _values_ (`system.context.values`) of the map.
+  If the property refers to a map (such as `system.contexts`), the hint either applies to the _keys_ of the map (`system.contexts.keys`) or the _values_ (`system.contexts.values`) of the map.
   This attribute is mandatory.
 
 | `values`