Fix build failure

Author: rujche

aad/spring-security/reactive/webflux/oauth2/spring-cloud-gateway/gateway/pom.xml

@@ -20,7 +20,7 @@
   <dependencies>
     <dependency>
       <groupId>org.springframework.cloud</groupId>
-      <artifactId>spring-cloud-starter-gateway</artifactId>
+      <artifactId>spring-cloud-starter-gateway-server-webflux</artifactId>
     </dependency>
     <dependency>
       <groupId>org.springframework.boot</groupId>