Fix pointcut for async controllers

We need @within (not @target) to capture method executions inside
annotated controllers. With @target all beans with methods returning
Callable get wrapped in case at runtime there is a target match.

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/TraceContextHolder.java

@@ -17,8 +17,8 @@
 package org.springframework.cloud.sleuth;
 
 import lombok.extern.apachecommons.CommonsLog;
+
 import org.springframework.core.NamedThreadLocal;
-import org.springframework.util.Assert;
 
 /**
  * @author Spencer Gibb

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/web/TraceWebAspect.java

@@ -64,11 +64,11 @@ public class TraceWebAspect {
 		this.trace = trace;
 	}
 
-	@Pointcut("@target(org.springframework.web.bind.annotation.RestController)")
+	@Pointcut("@within(org.springframework.web.bind.annotation.RestController)")
 	private void anyRestControllerAnnotated() {
 	}
 
-	@Pointcut("@target(org.springframework.stereotype.Controller)")
+	@Pointcut("@within(org.springframework.stereotype.Controller)")
 	private void anyControllerAnnotated() {
 	}