Fix E721 linting errors

[jklaise]

Some are false positives (see https://www.flake8rules.com/rules/E721.html), I don't think there is a more idiomatic way of checking that two objects are of the same (possibly unknown) type. See also PyCQA/pycodestyle#882.

[codecov]

Codecov Report

Merging #846 (2a63197) into master (c2f0a5a) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #846   +/-   ##
=======================================
  Coverage   81.98%   81.98%           
=======================================
  Files         159      159           
  Lines       10375    10375           
=======================================
  Hits         8506     8506           
  Misses       1869     1869           

Files Changed	Coverage Δ
alibi_detect/od/mahalanobis.py	73.88% <100.00%> (ø)
alibi_detect/utils/mapping.py	97.01% <100.00%> (ø)
alibi_detect/utils/pytorch/distance.py	88.63% <100.00%> (ø)
alibi_detect/utils/state/state.py	97.50% <100.00%> (ø)
alibi_detect/utils/tensorflow/distance.py	92.68% <100.00%> (ø)