Add factorial with while loop

[hasangenc0]

related with #29
This is my solution to the top of the others.

[codecov-io]

Codecov Report

Merging #30 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #30   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          14     14           
  Lines         201    207    +6     
  Branches       36     35    -1     
=====================================
+ Hits          201    207    +6

Impacted Files	Coverage Δ
src/functions/factorial.ts	100% <100%> (ø)	⬆️

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[codecov-commenter]

Codecov Report

Merging #30 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #30   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           18        14    -4     
  Lines          280       207   -73     
  Branches        41        35    -6     
=========================================
- Hits           280       207   -73     

Impacted Files	Coverage Δ
src/functions/factorial.ts	100.00% <100.00%> (ø)
src/functions/max.ts	100.00% <0.00%> (ø)
src/functions/index.ts	100.00% <0.00%> (ø)
src/functions/times.ts	100.00% <0.00%> (ø)
src/functions/average.ts	100.00% <0.00%> (ø)
src/functions/is-array.ts	100.00% <0.00%> (ø)
src/functions/is-number.ts	100.00% <0.00%> (ø)
src/functions/is-string.ts	100.00% <0.00%> (ø)
src/functions/is-undefined.ts
... and 3 more

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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