Fix neutral_element for AbstractArrays

[odow]

Closes #318

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.30%. Comparing base (a12311e) to head (ecdd5c5).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #320   +/-   ##
=======================================
  Coverage   90.29%   90.30%           
=======================================
  Files          22       22           
  Lines        2237     2238    +1     
=======================================
+ Hits         2020     2021    +1     
  Misses        217      217           

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[odow]

Something's up:

(base) oscar@MacBookPro MutableArithmetics % git push
remote: Internal Server Error
fatal: unable to access 'https://github.com/jump-dev/MutableArithmetics.jl.git/': The requested URL returned error: 500
(base) oscar@MacBookPro MutableArithmetics % git push
fatal: unable to access 'https://github.com/jump-dev/MutableArithmetics.jl.git/': Failed to connect to github.com port 443 after 2570 ms: Couldn't connect to server
(base) oscar@MacBookPro MutableArithmetics % git push
fatal: unable to access 'https://github.com/jump-dev/MutableArithmetics.jl.git/': The requested URL returned error: 502