Postgres: Regex support foreign characters

[JeffGuKang]

Fix issue #5293

[dplewis]

Can you add a test to prevent regression? It should work for mongo as welll

[JeffGuKang]

@dplewis Sure. I will update again following the contributing guide.

[codecov]

Codecov Report

Merging #5598 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #5598      +/-   ##
==========================================
- Coverage   94.05%   94.04%   -0.01%     
==========================================
  Files         143      143              
  Lines       10094    10095       +1     
==========================================
  Hits         9494     9494              
- Misses        600      601       +1

Impacted Files	Coverage Δ
...dapters/Storage/Postgres/PostgresStorageAdapter.js	96.9% <100%> (ø)	⬆️
src/RestWrite.js	93.49% <0%> (-0.18%)	⬇️

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[acinader]

@dplewis since we're in node here and not the browser, we don't need to add the lib xregexp.

Can just use RegExp with the 'u' flag. Here's a test to show it: https://runkit.com/arthur/regex-unicode-example

thanks for picking this up. It's important. I shoulda caught it....