[fix] Make tags type a Mapping

[JayH5]

This reduces type errors when using the library. For example, consider a file test.py like:

from aiodogstatsd import Client

tags = {"foo": "bar"}
Client(constant_tags=tags)

...then running mypy on it:

❯ mypy test.py
test.py:4: error: Argument "constant_tags" to "Client" has incompatible type "Dict[str, str]"; expected "Optional[Dict[str, Union[float, int, str]]]"
test.py:4: note: "Dict" is invariant -- see http://mypy.readthedocs.io/en/latest/common_issues.html#variance
test.py:4: note: Consider using "Mapping" instead, which is covariant in the value type
Found 1 error in 1 file (checked 1 source file)

With this change, mypy is happy. Without this change, it's necessary to annotate variables that hold tags with the typedefs.MTags type explicitly.

[codecov-io]

Codecov Report

Merging #14 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #14   +/-   ##
=======================================
  Coverage   96.44%   96.44%           
=======================================
  Files           7        7           
  Lines         225      225           
  Branches       16       16           
=======================================
  Hits          217      217           
  Misses          6        6           
  Partials        2        2

Impacted Files	Coverage Δ
aiodogstatsd/typedefs.py	100% <100%> (ø)	⬆️

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[Gr1N]

Hi!

Thank you for your contribution.

Everything looks fine, but please fix a few moments:

• update your commit message to [fix] <your message here>
• update CHANGELOG.md

[JayH5]

@Gr1N thanks for the library

I've made the requested changes

[Gr1N]

New version of the package just published to PyPI:

• https://github.com/Gr1N/aiodogstatsd/releases/tag/0.10.0
• https://pypi.org/project/aiodogstatsd/0.10.0/

Enjoy!