Handle ACCOUNT_ID_REQUIRED error and update some text

[oschwald]

MaxMind is renaming "user ID" to "account ID" for basic auth as we roll out multi-user accounts. In doing this, we will be updating the error code returned by the service from USER_ID_REQUIRED to ACCOUNT_ID_REQUIRED. This PR supports both the new and old error code. It also updates some references to "user ID". It does not change change the accessor on Minfraud as I was not sure how you wanted to handle that.

[coveralls]

Coverage remained the same at 98.347% when pulling f318da1 on oschwald:greg/account-id into 6b97c5d on kushniryb:master.

[kushniryb]

Hello @oschwald
Thank you, this is great 👍
I suppose we'll go with user_id for now so that it's compatible with both versions.