Fix typo in AfterReturningAdviceInterceptor JavaDoc

See gh-1382

spring-aop/src/main/java/org/springframework/aop/framework/adapter/AfterReturningAdviceInterceptor.java

@@ -26,7 +26,7 @@ import org.springframework.aop.AfterReturningAdvice;
 import org.springframework.util.Assert;
 
 /**
- * Interceptor to wrap am {@link org.springframework.aop.AfterReturningAdvice}.
+ * Interceptor to wrap an {@link org.springframework.aop.AfterReturningAdvice}.
  * Used internally by the AOP framework; application developers should not need
  * to use this class directly.
  *