NoValInForComprehension

Removes val from definitions in for-comprehension:

// before
for {
  n <- List(1, 2, 3)
  val inc = n + 1
} yield inc
// after
for {
  n <- List(1, 2, 3)
  inc = n + 1
} yield inc

The two syntaxes are equivalent and the presence of the val keyword has been deprecated since Scala 2.10.