Return ErrAborted in Mutate() #46
Description
The Mutate() method should return y.ErrAborted when the transaction is aborted for retry. Currently it is returning the gRPC status error which is difficult to catch by a caller. In comparison, Commit() is correctly returning y.ErrAborted when it happens.
Reference: https://discuss.dgraph.io/t/how-to-catch-erraborted-in-dgraph-go-client/4141/4