Fix typo in documentation

- As error handling sample is using `CustomErrorType`, fix
  description which mentions `CustomerErrorType`.

Author: jvalkeal

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -2035,7 +2035,7 @@ particular controller and/or exception type.
 ----
 
 In the example above, if `YourException` is thrown by a controller defined in the same
-package as `FooController`, a json representation of the `CustomerErrorType` POJO will be
+package as `FooController`, a json representation of the `CustomErrorType` POJO will be
 used instead of the `ErrorAttributes` representation.