Upgrade typescript to 3.7.3.

[josephmbeveridge]

Summary

Resolves #99

Updated Typescript version to 3.7.3 and confirmed that optional chaining works in fresh project.

Test Plan

Create a new component which takes in an optional prop:

import React from 'react';
import {Text} from 'react-native';

interface Props {
  optionalFunction?: () => void;
}

const Test = ({optionalFunction}: Props) => {
  optionalFunction?.();
  return <Text>Testing optional chaining</Text>;
};

export default Test;

Include this new component in App.tsx and test passing a valid or undefined function. If the function is defined then it should execute before rendering. Something simple like () => console.log('Optional changing works!') is an easy check.

Compatibility

OS	Implemented
iOS	✅
Android	✅

Checklist

• I have tested this on a device and a simulator
• I added the documentation in README.md
• I mentioned this change in CHANGELOG.md
• I updated the typed files (TS and Flow)
• I added a sample use of the API in the example project (example/App.js)