Test failing with InvalidSignatureError

[bcarreno]

Thank you so much for writing and maintaing the Gala gem!

Tests were passing in May 2018 (last commit) but if you run them today you'll get this error.

$ rake test
Run options: --seed 59087

# Running:

...EF.

Finished in 0.041877s, 143.2767 runs/s, 262.6740 assertions/s.

  1) Error:
Gala::PaymentTokenTest#test_decrypt:
Gala::PaymentToken::InvalidSignatureError: Unable to verify a valid chain of trust from signature to root certificate.
    /Users/Carreno/prj/gala/lib/gala/payment_token.rb:61:in `validate_signature'
    /Users/Carreno/prj/gala/lib/gala/payment_token.rb:30:in `decrypt'
    /Users/Carreno/prj/gala/test/payment_token_test.rb:43:in `test_decrypt'

The exception is raised because the call to OpenSSL::X509::Store#verify is returning false https://github.com/spreedly/gala/blob/master/lib/gala/payment_token.rb#L78

My guess the problem is in the certificate, which expired in 2016. You can check via:

$ openssl x509 -in test/fixtures/certificate.pem -text -noout | grep -A 2 Validity
        Validity
            Not Before: Oct 26 12:10:10 2014 GMT
            Not After : Nov 24 12:10:10 2016 GMT

[bcarreno]

If you're busy I can work on a PR next week.