Update zend-diactoros to v1.6
Update zend-diactoros to v1.6

This release contains a useful fix for Content-Length problems
that we have experienced before.

See https://github.com/zendframework/zend-diactoros/releases/tag/1.6.0.

datitisev/core,datitisev/core,datitisev/core,malayladu/core,Luceos/core,datitisev/core,malayladu/core,flarum/core,Luceos/core,malayladu/core,malayladu/core,Luceos/core,Luceos/core,flarum/core,flarum/core