bump version of nbconvert

[rkpattnaik780]

Bump version of nbconvert to fix the CVE issues introduced by mistune@2.0.3.

What changes were proposed in this pull request?

How was this pull request tested?

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[lresende]

@rkpattnaik780 could you please sign your commit?

[rkpattnaik780]

@rkpattnaik780 could you please sign your commit?

Done. The checks are also passing now!