In ct_search, setting `type = "services"` requires EB02 commodity scheme

[ChrisMuir]

Example, showing the current issue:

vals <- ct_search(reporters = "Canada",
                  partners = "Germany",
                  type = "services")
#> Error: API request failed, with status code [200]
#> Fail Reason: Invalid classification for trade type.

Performing a query with arg type = "services" requires that the current commodity db scheme being used by comtradr be "EB02". It's easy to make this adjustment prior to making the call to ct_search by running comtradr::ct_update_databases("EB02"), but at the very least the error message in the example above should be more helpful (should indicate what the issue is, and how to fix it using ct_update_databases).

This issue first came up in #5.

[ChrisMuir]

Fixed via commit cd25402.