fix: do not modify dayjs input arguments

[kzahel]

I noticed that when passing in an array of date formats:

"If you don't know the exact format of an input string, but know it could be one of many, you can use an array of formats."
(from https://day.js.org/docs/en/parse/string-format) it was actually modifying the input array. This seems pretty bad.

I'm not sure if your build supports the ... syntax. It could be changed to Object.assign or similar if you want.

[codecov]

Codecov Report

Merging #1529 (2f790ae) into dev (c5688f3) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev     #1529   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          176       176           
  Lines         1980      1982    +2     
  Branches       502       503    +1     
=========================================
+ Hits          1980      1982    +2     

Impacted Files	Coverage Δ
src/index.js	100.00% <100.00%> (ø)

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[iamkun]

this is a nice catch, however, ... syntax will result in a large increase of the bundle size, maybe we should looking for some other way to fix this.