Replace deprecated String.prototype.substr()

[CommanderRoot]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

String.prototype.substr() is deprecated so we replace it with String.prototype.slice() or String.prototype.substring() which work similarily but aren't deprecated.
.substr() probably isn't going away anytime soon but the change is trivial so it doesn't hurt to do it.

Breaking Changes

None

Additional Info

[codecov]

Codecov Report

Merging #1429 (ee1624a) into master (830fe2c) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1429   +/-   ##
=======================================
  Coverage   96.81%   96.81%           
=======================================
  Files          12       12           
  Lines        1131     1131           
  Branches      411      411           
=======================================
  Hits         1095     1095           
  Misses         27       27           
  Partials        9        9           

Impacted Files	Coverage Δ
src/utils.js	94.72% <100.00%> (ø)

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