README.md has invalid sample code for validations

[mattnesterenko]

Took a minute to figure out why I couldn't get validations working based on the sample, but it looks like the sample code has a bug with the validation promise.

It displays this u1.validate(function() {}):

    u1.validate(function() {
      if u1.isValid {
         //validated, perform business logic
      } else {
         //validation failed, dump validation errors to the console
         console.log(p1.errors)
      }
    });

When it should call u1.validate().then(function() {}) from the validate promise:

    u1.validate().then(function() {
      if u1.isValid {
         //validated, perform business logic
      } else {
         //validation failed, dump validation errors to the console
         console.log(p1.errors)
      }
    });

Thanks, Matt