FIX: DerivativesDataSink nondeterministic checksums fixed with niworkflows=~1.3.4

[oesteban]

Makes sure this bugfix to NiWorkflows gets distributed with the current LTS.

Supersedes/closes: #2421.
Links: nipreps/niworkflows#640.

Changes proposed in this pull request

Documentation that should be reviewed

[oesteban]

Some dependency issues have regressed:

ERROR: networkx 2.6.1 has requirement matplotlib>=3.3, but you'll have matplotlib 2.2.2 which is incompatible.
ERROR: networkx 2.6.1 has requirement numpy>=1.19, but you'll have numpy 1.15.4 which is incompatible.
ERROR: networkx 2.6.1 has requirement pandas>=1.1, but you'll have pandas 0.23.4 which is incompatible.
ERROR: networkx 2.6.1 has requirement scipy!=1.6.1,>=1.5, but you'll have scipy 1.1.0 which is incompatible.
ERROR: sphinx-rtd-theme 0.5.2 has requirement docutils<0.17, but you'll have docutils 0.17.1 which is incompatible.

I'll have to first check on the latest build of maint/20.2.x to see what's the problem here.