Fix problem with Set#member?
Fix problem with Set#member?

Ruby's built-in collections, like Array, use #== for checking equality
in #include? and #member?. Hamster::Set uses #eql? (it's the only way
to implement it in a performant way). This makes Set#member? use #eql?,
just like Set#include? does.

dzjuck/hamster,jack-nie/hamster,xaviershay/hamster