Update index.adoc

Author: AndreasVolkmann

docs/manual/src/docs/asciidoc/_includes/servlet/kotlin-configuration/index.adoc

@@ -4,7 +4,7 @@
 Spring Security Kotlin Configuration support has been available since Spring Security 5.3.
 It enables users to easily configure Spring Security using a native Kotlin DSL.
 
-NOTE: Spring Security provides https://github.com/spring-projects/spring-security/tree/master/samples/boot/kotlin[a sample applications] which demonstrates the use of Spring Security Kotlin Configuration.
+NOTE: Spring Security provides https://github.com/spring-projects/spring-security/tree/master/samples/boot/kotlin[a sample application] which demonstrates the use of Spring Security Kotlin Configuration.
 
 [[kotlin-config-httpsecurity]]
 == HttpSecurity