[ntuple, doc] Fix typo in format specification (NFC)
[ntuple, doc] Fix typo in format specification (NFC)

Co-authored-by: Philippe Canal <69612018eea270a331b01ca4491eb7b1b815033a@fnal.gov>
olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root