ValidationException should be called ValidationError

[sbarfurth]

This looks odd in the README:

failed;
// [
//   ValidationException { rule: { name: "string", ... } },
//   ValidationException { rule: { name: "minLength", ... } }
// ]

An array of exception doesn't make sense. These should be called ValidationError since that is what they are. This would also be in line with JavaScript's own naming, where Errors and not Exceptions are thrown. This is fairly unique in JS, but in this case it makes sense to use Error.