delete请求传body数据 有兼容问题

#### Which platform are you running AnyProxy
Mac

#### The version of the AnyProxy
4.1.0

#### Your expected behavior of AnyProxy
delete请求传body数据,正常

#### The actual behavior of AnyProxy
代理服务器没有接受到body数据

#### 相关链接
希望对delete存在body的时候，在fetchRemoteResponse方法中兼容。
设置Response.headers里面的content-length
https://stackoverflow.com/questions/35589109/node-http-delete-request-no-longer-works-after-upgrading-from-0-10-40

Start at the fetchRemoteResponse method named in the issue and reproduce a DELETE request with a body on AnyProxy 4.1.0. Inspect how the response headers are populated, especially content-length. Done means the proxy receives the DELETE body and the relevant response header is set correctly.

Written by the indexing model from the issue text.