server::Builder stream/connection window size methods work by reference

[sfackler]

All of the other setters on the builder type operate by-value, but http2_initial_connection_window_size and http2_initial_stream_window size work by-reference.

[seanmonstar]

Ah man, that's an unfortunate mistake. I'll assign this breaking change to be done in 0.13.

[seanmonstar]

As an interim, we could add new methods that are by-value, with an underscore prefix... 🤷‍♂️