Correct typo: Rename ArrayIndex::indexs to ArrayIndex::indexes

[alamb]

The correct spelling of the English plural form of index is indexes or indicies -- I chose to go with indexes as it is closer to the original in the code

This was added in #419

[coveralls]

Pull Request Test Coverage Report for Build 2300260078

• 9 of 9 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 90.425%

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Totals
Change from base Build 2300062609:	0.0%
Covered Lines:	8254
Relevant Lines:	9128

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💛 - Coveralls