hamster wheel: avoid deprecated "encoding" msgpack param

"encoding" was deprecated in msgpack module.

raw_as_bytes was added in 0.5.2 and is recommended going forward,
but it's not clear to me if we have any reason to specify it.

ref msgpack/msgpack-python@5534d0c#diff-88b99bb28683bd5b7e3a204826ead112R40

README.md

@@ -56,13 +56,23 @@ See the [Python Plugin API](http://pynvim.readthedocs.io/en/latest/usage/python-
 
 #### Development
 
-If you change the code, you need to run
-```sh
-pip2 install .
-pip3 install .
-```
-for the changes to have effect. For instructions of testing and troubleshooting,
-see the [development](http://pynvim.readthedocs.io/en/latest/development.html) documentation.
+Use (and activate) a local virtualenv.
+
+    python3 -m venv env36
+    source env36/bin/activate
+
+If you change the code, you must reinstall for the changes to take effect:
+
+    pip install .
+
+Use `pytest` to run the tests. Invoking with `python -m` prepends the current
+directory to `sys.path` (otherwise `pytest` might find other versions!):
+
+    python -m pytest
+
+For details about testing and troubleshooting, see the
+[development](http://pynvim.readthedocs.io/en/latest/development.html)
+documentation.
 
 #### Usage through the python REPL
 

docs/development.rst

@@ -19,9 +19,11 @@ in order for Neovim to use it for the plugin host.
 
 To run the tests execute::
 
-    pytest
+    python -m pytest
+
+This will run the tests in an embedded instance of Neovim, with the current
+directory added to ``sys.path``.
 
-This will run the tests in an embedded instance of Neovim.
 If you want to test a different version than ``nvim`` in ``$PATH`` use::
 
     NVIM_CHILD_ARGV='["/path/to/nvim", "-u", "NONE", "--embed"]' pytest
@@ -30,7 +32,7 @@ Alternatively, if you want to see the state of nvim, you could use::
 
     export NVIM_LISTEN_ADDRESS=/tmp/nvimtest
     xterm -e "nvim -u NONE"&
-    pytest
+    python -m pytest
 
 But note you need to restart Neovim every time you run the tests!
 Substitute your favorite terminal emulator for ``xterm``.

pynvim/msgpack_rpc/msgpack_stream.py

@@ -20,8 +20,7 @@ class MsgpackStream(object):
     def __init__(self, event_loop):
         """Wrap `event_loop` on a msgpack-aware interface."""
         self.loop = event_loop
-        self._packer = Packer(encoding='utf-8',
-                              unicode_errors=unicode_errors_default)
+        self._packer = Packer(unicode_errors=unicode_errors_default)
         self._unpacker = Unpacker()
         self._message_cb = None