FIX: Fix body length changed

[hamlet-lee]

In current implementation, when downstream posts a content with "\r\n", the body length is changed.
Which makes request proxied to upstream has "Content-Length" > body length
So upstream server will wait forever (until timeout) for the request.

I have tested this pull request.

[puneetjaiswal]

Awesome debugging - https://github.com/hamlet-lee/blog/blob/master/2019-05-22.md 👍

[hamlet-lee]

@puneetjaiswal my pleasure :)