fix: isMobilePhone Regular Expression for Vietnamese phone number

[luisrivas]

According to this Vietnam phone number guide, we should accept 11 length phone numbers as valid when the number starts with the 84 country code. In addition, I am adding the 55 area code.

Closes #813

Checklist

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

[profnandaa]

LGTM, please fix the merge conflicts and we should be good to go.

[codecov]

Codecov Report

Merging #1689 (c0f9b3c) into master (01eeaef) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master     #1689   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          101       101           
  Lines         1862      1862           
=========================================
  Hits          1862      1862           

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

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[luisrivas]

Fixed! @profnandaa