Fix all flake8 issues except for E501 (line too long)

[blag]

No description provided.

[codecov-io]

Codecov Report

Merging #101 into master will increase coverage by 1.19%.
The diff coverage is 84.84%.

@@            Coverage Diff             @@
##           master     #101      +/-   ##
==========================================
+ Coverage   93.58%   94.78%   +1.19%     
==========================================
  Files          13       13              
  Lines         998      997       -1     
==========================================
+ Hits          934      945      +11     
+ Misses         64       52      -12

Impacted Files	Coverage Δ
jose/backends/pycrypto_backend.py	96.36% <ø> (ø)	⬆️
jose/jwk.py	95.12% <100%> (ø)	⬆️
jose/jwt.py	100% <100%> (+5.8%)	⬆️
jose/backends/ecdsa_backend.py	98.66% <100%> (ø)	⬆️
jose/backends/cryptography_backend.py	97.86% <100%> (ø)	⬆️
jose/backends/rsa_backend.py	97.2% <100%> (ø)	⬆️
jose/__init__.py	100% <100%> (ø)	⬆️
jose/backends/__init__.py	36.36% <40%> (ø)	⬆️
jose/jws.py	96.63% <85.71%> (+2.52%)	⬆️

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[mpdavis]

lgtm