Does the Shadow Blade spell add dex/str as appropriate when dealing damage?

@JeremyECrawford does the shadow blade from the eponymous spell add dex/str as appropriate when dealing damage or is it only the flat 2d8 psychic damage?

— PKMN Trainer Tom (@IFlyDragons) November 14, 2017

The shadow blade spell creates a weapon, and the spell doesn't tell you to ignore the general rule on making weapon attacks (PH, 195). You therefore add the appropriate ability modifier. #DnD https://t.co/gAmiVnM5jP

— Jeremy Crawford (@JeremyECrawford) November 14, 2017