fix(type-guards): fix user-defined type guards

[trxcllnt]

also ran prettier on everything, so there's that :/

closes #44 for real now tho

Description:

Related issue (if exists):

[patsissons]

The change appears to have broken some generated predicate signatures? my 2.3.0 single.ts module has required predicate param instead of optional.

// node_modules/ix/add/iterable-operators/single.ts
export function singleProto<T, S extends T>(
  this: IterableX<T>,
  predicate: (value: T, index: number) => value is S
): S | undefined;
export function singleProto<T>(
  this: IterableX<T>,
  predicate: (value: T, index: number) => boolean
): T | undefined;
export function singleProto<T>(
  this: IterableX<T>,
  predicate: (value: T, index: number) => boolean = () => true
): T | undefined {
  return single(this, predicate);
}

[trxcllnt]

@patsissons ah shit, thanks for reporting. will review the rest of the changes here and do a patch release with all the fixes