[Http1Layer]: Upgrade h11 version to 0.6.0.

[mike820324]

Based on this discussion,
https://github.com/njsmith/h11/issues/17#issuecomment-256278531

I think we should bump the h11 version to 0.6.0.
The most important part would be remove the keep_case parameter.

[mike820324]

Resolved via #206