cannot access org.apache.http.annotation.Immutable

现象：
[ERROR] diagnostic: error: cannot access org.apache.http.annotation.Immutable
  class file for org.apache.http.annotation.Immutable not found

分析：
预计是兼容性问题
具体见：https://github.com/spring-projects/spring-boot/issues/6662

处理：
<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<exclusions>
<exclusion>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpcore</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpcore</artifactId>
<version>4.4.4</version>
</dependency>