fix v1.7 deprecations

[ChrisRackauckas]

WARNING: Wrapping `Vararg` directly in UnionAll is deprecated (wrap the tuple instead).

[codecov]

Codecov Report

Merging #178 (3c831db) into master (90c269f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #178   +/-   ##
=======================================
  Coverage   83.63%   83.63%           
=======================================
  Files          11       11           
  Lines        1644     1644           
=======================================
  Hits         1375     1375           
  Misses        269      269           

Impacted Files	Coverage Δ
src/array_index.jl	97.38% <ø> (ø)

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