Fix Money#== and Ruby 2.2 deprecation warning

[jimpo]

#470 made a breaking change to the behavior of Money#==. This reverts the change in #470 while still removing the deprecation warning.

Ruby 2.2 warns that <=> should return nil on invalid comparisons rather than raise an error.

Fixes #469.

[semmons99]

Waiting for all my green lights, then I'll merge.

[printercu]

@jimpo @semmons99 there are warning after this pr was merged:

~/.rvm/gems/ruby-2.2.1/gems/rspec-expectations-3.2.1/lib/rspec/matchers/built_in/eq.rb:35: warning: Return nil in #<=> if the comparison is inappropriate or avoid such comparison.

[jimpo]

Interesting. Is that in the test suite for this gem or another application? Could you show the line in your application that caused it?

[printercu]

i've run rspec in gem

[semmons99]

Yeah. Please provide more info as we're not able to reproduce locally or on CI.

[jimpo]

It issues the warning in Ruby 2.2.1, not Ruby 2.2.2. The issue is that Money#<=> is throwing a Money::Bank::UnknownRate error when comparing two non-zero amounts with different currencies in the test suite.

I guess we need to decide what the behavior of Money#== should be in this case. money1.eql?(money2) is false because the currencies are not the same, but if an exchange rate is defined and the converted amounts are equal, money1 <=> money2 == 0. money1 == money2 could either always be false if the currencies are different and the amounts are nonzero, or it could possibly raise a Money::Bank::UnknownRate error. Thoughts?

[semmons99]

Can you open another ticket and ping all collabs? Also, feel free to submit a PR that just does what you think it should 😄

[jimpo]

Continuing discussion here.