[REVIEW] revert cuco to latest dev branch, issues should be fixed

[ChuckHastings]

We had an issue in CI that uncovered the fact that raft is referencing the dev branch of coco while cugraph has it pinned to a previous commit. CI is using the newer dev branch version, which doesn't match what happens when we do local builds.

The original motivation for pinning was a temporary fix because of a bug introduced in coco which has since been resolved. This PR reverts us back to using the dev branch.

[codecov-commenter]

Codecov Report

Merging #1721 (10d7467) into branch-21.08 (9bcfa14) will increase coverage by 0.02%.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           branch-21.08    #1721      +/-   ##
================================================
+ Coverage         59.82%   59.85%   +0.02%     
================================================
  Files                77       77              
  Lines              3515     3517       +2     
================================================
+ Hits               2103     2105       +2     
  Misses             1412     1412              

Impacted Files	Coverage Δ
python/cugraph/_version.py	44.80% <0.00%> (+0.39%)	⬆️

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[ChuckHastings]

rerun tests

[BradReesWork]

@gpucibot merge