message: Add missing DOI
diff: @@ -30,6 +30,7 @@ journal = {Foundations of Computational Mathematics},
  number = {6},
  pages = {1333--1396},
  publisher = {Springer-Verlag},
  +doi = {10.1007/s10208-017-9370-z},
  title = {{Structure and stability of the one-dimensional Mapper}},
  volume = {18},
  year = {2017}
  @@ -47,6 +48,7 @@ journal = {Foundations of Computational Mathematics},
  number = {1},
  pages = {79--103},
  publisher = {Springer-Verlag},
  +doi = {10.1007/s10208-008-9027-z},
  title = {{Extending persistence using Poincar{\'{e}} and Lefschetz duality}},
  volume = {9},
  year = {2009}
  