feat(isEmail): add host_whitelist option

[TomScavo]

Add host whitelist option to only allow users to enter some specific email domains.
Fixes #1912

Checklist

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

[codecov]

Codecov Report

Merging #1927 (2130154) into master (f055c11) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1927   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          102       103    +1     
  Lines         2072      2078    +6     
  Branches       472       475    +3     
=========================================
+ Hits          2072      2078    +6     

Impacted Files	Coverage Δ
src/lib/isEmail.js	100.00% <100.00%> (ø)
src/lib/isURL.js	100.00% <100.00%> (ø)
src/lib/util/checkHost.js	100.00% <100.00%> (ø)

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[profnandaa]

Duplicate of #1920