Use custom json schema faker.

[ksaaskil]

• Allows using unmock in React Native (https://github.com/unmock/unmock-react-native-example/pull/3)
• Use @meeshkanml/json-schema-faker from the unmock branch of json-schema-faker fork
• The custom fork adds (1) react-native field pointing to dist/index.js instead of the browser build and (2) custom json-schema-ref-parser excluding http and https in the browser build
• Update the import of json-schema-faker to use the default if available. This approach seems to be the only way to get jsf is of correct type in Node.js, browser, and React Native. There could be something wrong with the json-schema-faker builds but I'd rather not start hacking those now.

[codecov-io]

Codecov Report

Merging #360 into dev will decrease coverage by 0.01%. The diff coverage is 75%.

@@            Coverage Diff             @@
##              dev     #360      +/-   ##
==========================================
- Coverage   80.39%   80.38%   -0.02%     
==========================================
  Files          54       54              
  Lines        2413     2416       +3     
  Branches      583      585       +2     
==========================================
+ Hits         1940     1942       +2     
- Misses        473      474       +1

Impacted Files	Coverage Δ
packages/unmock-core/src/generator.ts	87.4% <75%> (-0.24%)	:arrow_down:

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