Array#uniq to correctly identify == GlobalIDs

[fattymiller]

When performing an Array#uniq with two GlobalID objects that are ==, the result of the uniq still contains the "duplicate" entries.

This PR changes the hash method to consider the hash of the underlaying URI hash so that two GlobalID objects pointing to the same object are considered duplicates of each other.

Previously, with:
p1 = GlobalID.create(Person.new(1))
p2 = GlobalID.create(Person.new(1))

p1 == p2 #=> true but [p1, p2].uniq #=> [p1, p2]

[rails-bot]

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