fix(isMobilePhone): update phone regex for Zambia

[imkrishh]

Updated Zambia phone number RegEx validator

Added support for new phone network provider for Zambia [ref-link]
077 - Airtel (New Serial #)
076 - MTN (New Serial #)

Checklist

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

[codecov]

Codecov Report

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

Coverage data is based on head (f21d839) compared to base (86a07ba).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##            master     #2037    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          104       104            
  Lines         2203      2308   +105     
  Branches       477       578   +101     
==========================================
+ Hits          2203      2308   +105     

Impacted Files	Coverage Δ
src/lib/isMobilePhone.js	100.00% <ø> (ø)
src/lib/isIP.js	100.00% <0.00%> (ø)
src/lib/isIn.js	100.00% <0.00%> (ø)
src/lib/trim.js	100.00% <0.00%> (ø)
src/lib/alpha.js	100.00% <0.00%> (ø)
src/lib/isBIC.js	100.00% <0.00%> (ø)
src/lib/isEAN.js	100.00% <0.00%> (ø)
src/lib/isHSL.js	100.00% <0.00%> (ø)
src/lib/isInt.js	100.00% <0.00%> (ø)
src/lib/isJWT.js	100.00% <0.00%> (ø)
... and 83 more

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[pano9000]

Hi @imkrishh,

thanks for the PR.
For future reference, here's also the ITU numbering plan, which is always a more accurate reference than a Wikipedia entry:
https://www.itu.int/dms_pub/itu-t/oth/02/02/T02020000E80006PDFE.pdf

It looks like currently only the following ranges are assigned and valid, which your PR is implementing, so thanks!
75, 76, 77
95, 96, 97

Also another reference for the future:
Real world random examples from Google Maps for those of these numbers
https://goo.gl/maps/4sNtcZAWjzkZKnin7
+260 97 xxxxxxx

https://goo.gl/maps/YbE5RygVAwBarQhj7
+260 76 xxxxxxx

Justone thing, that I think still needs to be done ideally:
Could you kindly also add an additional test for one of these new numbers into the tests as well?

Thanks!

---

for future reference:
there is another (unrelated to this PR) issue with the en-ZM RegExp, but that is rather part of the discussion in #2124, so that shouldn't stop this PR from being merged after the updated tests are provided

[pano9000]

thank you.
looks good to me now :-)
However please note, I don't have any privileges in this project, so we will have to wait for two of the maintainers to review and merge this.

[profnandaa]

LGTM. can fix the merge conflict if possible, or I'll fix them during clean-up.

[rubiin]

@imkrishh can you fix the merge conflicts