quantile: rename interpolation kwarg to method

[mathause]

numpy v1.22.0 introduces some changes to np.quantile it renames the interpolation keyword to method. This PR restores compatibility with numpy 1.22.

• Passes isort . && black . && flake8
• Fully documented, including CHANGELOG.rst

[codecov-commenter]

Codecov Report

Merging #137 (13562fe) into master (a682256) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #137      +/-   ##
==========================================
+ Coverage   78.97%   79.05%   +0.07%     
==========================================
  Files          29       29              
  Lines        1346     1351       +5     
==========================================
+ Hits         1063     1068       +5     
  Misses        283      283              

Flag	Coverage Δ
unittests	79.05% <100.00%> (+0.07%)	⬆️

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Impacted Files	Coverage Δ
mesmer/calibrate_mesmer/train_gv.py	85.33% <100.00%> (+0.40%)	⬆️
mesmer/create_emulations/create_emus_gv.py	73.46% <0.00%> (+1.73%)	⬆️

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