Targeting the Semaphore libraries to ES6

[cedoor]

The current Semaphore libraries are written in TypeScript and are "compiled" into JavaScript with Rollup and tsc. The target in the current tsconfig.ts configuration is ES5, i.e. the first major revision to JavaScript.

Targeting ES6 (ECMAScript 2015) should be generally fine today. It's widely supported across modern browsers and environments and it would allow Semaphore bundles to use many ES6 features natively, like arrow functions, promises, and classes, which can improve code readability and efficiency.

[vplasencia]

Hey! I agree. We could also use a version later than ECMAScript 2015.

[cedoor]

Most modern browsers should also support ES2020 features. I took a look at https://caniuse.com, and it seems to confirm it. Users who are currently using browsers that don't support ES2020 are usually < 1%.