Support Python 2.7

[rossmacarthur]

No description provided.

[codecov-io]

Codecov Report

Merging #35 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #35   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           6      6           
  Lines         494    504   +10     
=====================================
+ Hits          494    504   +10

Impacted Files	Coverage Δ
src/serde/error.py	100% <100%> (ø)	⬆️
src/serde/model.py	100% <100%> (ø)	⬆️
src/serde/field.py	100% <100%> (ø)	⬆️
src/serde/validate.py	100% <100%> (ø)	⬆️
src/serde/__init__.py	100% <100%> (ø)	⬆️
src/serde/util.py	100% <100%> (ø)	⬆️

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