Enable the `require-await` ESLint rule

The require-await ESLint rule requires that async functions have at least one await expression in their bodies. I think this makes sense, since the majority of the time, that is the main reason why you'd want to mark a function as async: to use await.

The main reason not to enable this rule is apparently if you want to allow this shorthand way of ensuring that a function which throws an error returns a rejected promise, rather than unwind the call stack.

Perhaps that's desirable, but it strikes as as very implicit and non-obvious.