Bump nerval to latest rc

This will fix the evaluation issue when the model predicts empty lines. These are also present in the BIO files and nerval doesn't support it until 0.3.3-rc1.

changed milestone to %DAN-P6: Training improvements Part 2

added P2 label

requested review from @mboillet

assigned to @yschneider

approved this merge request

merged

mentioned in commit 01e29d59