Prevent PayPal SDK expection parsing bug

PayPal SDK ServerError exception class crashes
if you ask for a message or inspect. Catch the exception
and instead log a general error msg precenting the crash.
The crash is because it always tries to parse the response
body as json and sometimes world is not entirely made of json.
Narrow rescue scope from Exception to StandardError
Merge pull request #651 from sharetribe/paypal-error-crash

Prevent PayPal SDK expection parsing bug