BibRank: increase rnkDOWNLOADS.file_format size

* Increses the size of the file_format column in rnkDOWNLOADS
  since this might contain both the format and subformat information.

Co-authored-by: Tibor Simko <tibor.simko@cern.ch>
Merge branch 'master' into next

* master:
  BibRank: increase rnkDOWNLOADS.file_format size

* Merge note: amended RnkDOWNLOADS model accordingly.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>