Upgrade to TypeScript v4

[kindlyfire]

Expected Behavior

SDK should compile on the latest stable version of TypeScript

Current Behavior

SDK does not compile on TypeScript v4

Possible Solution

Update TypeScript code to support v4 and update TypeScript dependency in package.json
For projects currently using the JS SDK, using TypeScript v3 is a solution until the JS SDK gets an update.

[scottinet]

Thanks for noticing. I triaged this issue so it can be resolved quickly.