Thread safety by using the default source for the RNG

[ridv]

• Using custom sources results in the RNG becoming non-thread safe. Using the default source guarantees that multiple threads are able to generate data using faker safely as per the Go docs (https://golang.org/pkg/math/rand/).

[codecov]

Codecov Report

Merging #23 into master will decrease coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #23      +/-   ##
==========================================
- Coverage   97.85%   97.82%   -0.04%     
==========================================
  Files           8        8              
  Lines         373      367       -6     
==========================================
- Hits          365      359       -6     
  Misses          4        4              
  Partials        4        4

Impacted Files	Coverage Δ
address.go	100% <100%> (ø)	⬆️
payment.go	100% <100%> (ø)	⬆️
faker.go	95.2% <100%> (+0.02%)	⬆️
internet.go	100% <100%> (ø)	⬆️

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[agoalofalife]

@rdelval the tests all passed successfully
good)

[agoalofalife]

@rdelval have you checked it manually?

[ridv]

Yup checked it manually with very heavy use (50 threads running 1000 iterations generating a good amount of data), as well as running with the -race flag.

By the way, I should mention this might change some of the results for the benchmarks. So if that's important, we should do a benchmark test on the same machine of the non-thread safe version vs the thread safe version and make a decision based on data.

[agoalofalife]

@rdelval excellent, thanks for the contribution)