Add Validated.ensure

[markus1189]

Adds the ensure method known from Xor to Validated:

scala> Validated.valid("").ensure(new IllegalArgumentException("Must not be empty"))(_.nonEmpty)
res0: Validated[IllegalArgumentException,String] = Invalid(java.lang.IllegalArgumentException: Must not be empty)

[codecov-io]

Current coverage is 90.87%

Merging #984 into master will not affect coverage as of 869f4ce

@@            master    #984   diff @@
======================================
  Files          181     181       
  Stmts         2160    2160       
  Branches        42      43     +1
  Methods          0       0       
======================================
  Hit           1963    1963       
  Partial          0       0       
  Missed         197     197       

Review entire Coverage Diff as of 869f4ce

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[ceedubs]

Alternatively I think this could be if (x.exists(i => !(p(i)))). What's here is totally fine for a test though.

[ceedubs]

👍 thanks @markus1189!

[markus1189]

I like your suggestion using exists better ;)

[stew]

👍