fix error in README example

[dmitrytarassov]

There is an error in your example in the README. The expression validate().then(console.log("Valid List.")) will log Valid List. to the console regardless of whether the function completes successfully or throws an error. The correct approach is to pass a function to then that will be executed when the promise is resolved, instead of calling the function immediately.

// WRONG
validate()
  .then(console.log("Valid List."))
  .catch(console.error)

// CORRECT
validate()
  .then(() => console.log("Valid List."))
  .catch(console.error)