Fixed Iterator#uniq with block

[maiha]

Current implementation works only with block : T -> T, otherwise it breaks.

master : Crystal 0.20.3+40 [a62dff3] (2016-12-30)

(1..3).each.uniq(&.+ 1).next   # => 1
(1..3).each.uniq(&.even?).next

instantiating 'Iterator::Uniq(Range::ItemIterator(Int32, Int32), Int32, Bool)#next()'
in /home/maiha/git/maiha/crystal/src/iterator.cr:1025: no overload matches 'Hash(Int32, Bool)#[]=' with types Bool, Bool
Overloads are:
 - Hash(K, V)#[]=(key : K, value : V)

          @hash[transformed] = true

This PR : Crystal 0.20.3+41 [d9fca7b] (2016-12-30)

• Fixed code to keep flags with U
• Fixed spec to use block T -> U rather than T -> T

(1..3).each.uniq(&.+ 1).next   # => 1
(1..3).each.uniq(&.even?).next # => 1

Thanks.

[asterite]

Good catch, thank you! ❤️