Log Message:
Update net/py-hpack to 2.0.1.

Changes:
2.0.1 (2015-11-09)
------------------
Fixed a bug where the Python HPACK implementation would only emit header table
size changes for the total change between one header block and another, rather
than for the entire sequence of changes.

2.0.0 (2015-10-12)
------------------
Remove unused HPACKEncodingError.
Add the shortcut ability to import the public API (Encoder, Decoder, HPACKError,
HPACKDecodingError) directly, rather than from hpack.hpack.