If your divorce became final on or before December 31, 2018, you're not married for that year. Answer No to the Were you married? question.
On the other hand, if your divorce wasn't finalized until after December 31, you'd answer Yes.
NOTE: For finalized divorces, if you filed married filing jointly (MFJ) last year, start a return in a new account this year. Completely removing a spouse after transferring information from a previous years' return is really tricky and something inappropriate is likely to be left in.