Update failing PayPal remote refund test

In August 2010 PayPal updated how refunding Purchases work, so that they retained the Fixed Fee portion of the Purchase Payment Fee (the $0.30 in 2.9% + 0.30).
Merge pull request #1438 from Shopify/fix-paypal-remote-test-for-transaction-fee-refunds

Update failing PayPal remote refund test