Either combine or deprecate different implementations for fetching customers

[pulkitsinghal]

This example is one of many ways in which we can change our implementation to support all versions of the Vend API. It is not a solution which fits all situations, it just happened to be a simple usecase where altering path sufficed.

Anyway, we have two implementations: fetchCustomers and fetchCustomers2 and we should spend some time to either completely remove the 0.x endpoint or come up with an elegant way to support it both for the consumers of our SDK and in our implementation.