Ref #563 - return unique validation errors

[zoul0813]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  feature/bug fix?

• What is the current behavior? (You can also link to an open issue here)
  Every validator returns the "this field is required!" message when using multiple validators on required fields

• What is the new behavior (if this is a feature change)?
  The errors array is run through Lodash's uniq() function to remove duplicate messages

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  It should not, but if anyone has come up with ways of dealing with duplicate validation errors this may cause problems... ?

• Other information:
  Closes when use multiple validations show multiple errors #563