1.4.1 doCreateCustomer update doesn't account for Customer being passed as argument

[beattie19]

This line of code assumes that $customer is an array. However, it can be a Customer or an array.

Implementing this version upgrade in our codebase caused issues for us because we are passing a Customer object to createCustomer and resulted in the following error: Cannot use object of type Eway\Rapid\Model\Customer as array.

Originally posted by @beattie19 in #26 (comment)