Polish "Fix typo in logback example"

See gh-18295

Author: mbhave

spring-boot-project/spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -1325,7 +1325,7 @@ Your logback configuration file can also make use of System properties that the
 * `$\{LOG_EXCEPTION_CONVERSION_WORD}`: Whether `logging.exception-conversion-word` was set in Boot's external configuration.
 
 Spring Boot also provides some nice ANSI color terminal output on a console (but not in a log file) by using a custom Logback converter.
-See the `CONSOLE_LOG_PATTERN` in the `default.xml` configuration for an example.
+See the `CONSOLE_LOG_PATTERN` in the `defaults.xml` configuration for an example.
 
 If Groovy is on the classpath, you should be able to configure Logback with `logback.groovy` as well.
 If present, this setting is given preference.