I wrote the following sentence in an answer to an anonymous reviewer:
We would like to thank again the reviewer for the positive review and hope that the new version of the text meets their expectations.
I don't know if the reviewer is male or female. So, I thought that I could use their instead of his or her following what is explained here.
My co-author, seems to think that it is wrong to write it like that.
Is he right? If yes, how can I transform my sentence into a correct one?