feat(isMobilePhone): Add regex for Somalia so-SO

[ohersi]

Added regex validation for Somalia (so-SO) mobile phone numbers, country codes referenced from these documents:

• THE NATIONAL TELEPHONE NUMBERING PLAN by National Communications Authority - Federal Republic of Somalia
• NUMBERING REGULATION by National Communications Authority - Federal Republic of Somalia

Checklist

• PR contains only changes related; no stray files, etc.
• README updated (where applicable)
• Tests written (where applicable)

[profnandaa]

This LGTM, we're just about to make our next release and the preps are done. Unfortunately this will miss the train but should be on the next one.

Please fix the merge conflicts.

[ezkemboi]

LGTM.
Please check @rubiin @profnandaa @tux-tn

[codecov]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (f89e0a8) compared to base (54d330c).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2175   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          105       105           
  Lines         2324      2324           
  Branches       586       586           
=========================================
  Hits          2324      2324           

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

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