Used the *= operator by factorial.ts

[christianbender]

After my change I ran the tests successful.

[codecov]

Codecov Report

Merging #56 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #56   +/-   ##
=======================================
  Coverage   65.34%   65.34%           
=======================================
  Files         143      143           
  Lines        3714     3714           
  Branches      350      350           
=======================================
  Hits         2427     2427           
  Misses       1266     1266           
  Partials       21       21

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

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