Ensure no base64 incorrect padding errors occur in PY3

[ralphje]

Using a Kubernetes oid token configuration with Python 3, I encountered incorrect padding errors when the library attempted to decode the base64 string. Looking into the code base, I noticed that == is added to avoid this error in Python 2, but is mysteriously omitted from the Python 3 call.

I'm not sure why this is, especially since Python 3 has the exact same behaviour regarding insufficient padding as Python 2. Since the trick with adding == still works in Python 3, I have simply copied this from the Python 2 implementation and added a comment why this magic constant works.

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[codecov-io]

Codecov Report

Merging #132 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #132   +/-   ##
=======================================
  Coverage   92.84%   92.84%           
=======================================
  Files          13       13           
  Lines        1328     1328           
=======================================
  Hits         1233     1233           
  Misses         95       95

Impacted Files	Coverage Δ
config/kube_config.py	86.37% <ø> (ø)	⬆️

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[ralphje]

Appears to duplicate #79, though my fix was a more simple approach.