Bump msgpack version

[pardo]

If you are using the latest msgpack will break when trying to retrieve data

encoding option is removed. UTF-8 is used always.

https://github.com/msgpack/msgpack-python#major-breaking-changes-in-msgpack-10

Not sure how the bump and the code change might affect msgpack-pypy

~/.cache/pypoetry/virtualenvs/project-6gE1vKXj-py3.8/lib/python3.8/site-packages/scrapinghub/hubstorage/serialization.py in mpdecode(iterable)
     26 
     27 def mpdecode(iterable):
---> 28     unpacker = Unpacker(encoding='utf8')
     29     for chunk in iterable:
     30         unpacker.feed(chunk)

msgpack/_unpacker.pyx in msgpack._cmsgpack.Unpacker.__init__()

TypeError: __init__() got an unexpected keyword argument 'encoding'

[codecov]

Codecov Report

Merging #147 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #147   +/-   ##
=======================================
  Coverage   93.96%   93.96%           
=======================================
  Files          28       28           
  Lines        1938     1938           
=======================================
  Hits         1821     1821           
  Misses        117      117

Impacted Files	Coverage Δ
scrapinghub/hubstorage/serialization.py	97.14% <100%> (ø)	⬆️
scrapinghub/client/utils.py	94.25% <0%> (ø)	⬆️
scrapinghub/hubstorage/batchuploader.py	94.15% <0%> (ø)	⬆️
scrapinghub/legacy.py	98.41% <0%> (ø)	⬆️
scrapinghub/hubstorage/resourcetype.py	97.35% <0%> (ø)	⬆️

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[vshlapakov]

@pardo Looks good to me, thanks!