[REF] Removes .get_data() nibabel calls

[rmarkello]

Deprecated as of 3.0 in favor of np.asarray(img.dataobj).

[coveralls]

Pull Request Test Coverage Report for Build 332

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 91.388%

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Totals
Change from base Build 330:	0.005%
Covered Lines:	17318
Relevant Lines:	18950

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💛 - Coveralls

[codecov]

Codecov Report

Merging #120 into master will not change coverage.
The diff coverage is 88.88%.

@@           Coverage Diff           @@
##           master     #120   +/-   ##
=======================================
  Coverage   91.45%   91.45%           
=======================================
  Files          33       33           
  Lines        1895     1895           
=======================================
  Hits         1733     1733           
  Misses        162      162

Impacted Files	Coverage Δ
abagen/tests/test_allen.py	100% <100%> (ø)	⬆️
abagen/samples.py	100% <100%> (ø)	⬆️
abagen/utils.py	92.56% <83.33%> (ø)	⬆️

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