Fix nonzero warning

[wHao-Wu]

[Fix]: Fix warning of deprecated usages of nonzero during training with pytorch 1.6 (#320 )

• fix warning caused by upgrade of pytorch by specifying as_tuple=Fasle

[codecov]

Codecov Report

Merging #330 (d00244b) into master (ccd3047) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #330   +/-   ##
=======================================
  Coverage   49.69%   49.69%           
=======================================
  Files         174      174           
  Lines       11757    11757           
  Branches     1838     1838           
=======================================
  Hits         5843     5843           
  Misses       5554     5554           
  Partials      360      360           

Flag	Coverage Δ
unittests	49.69% <0.00%> (ø)

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Impacted Files	Coverage Δ
mmdet3d/models/dense_heads/anchor3d_head.py	61.85% <ø> (ø)
mmdet3d/models/dense_heads/ssd_3d_head.py	13.93% <0.00%> (ø)
mmdet3d/models/dense_heads/train_mixins.py	6.47% <ø> (ø)
...det3d/models/roi_heads/bbox_heads/h3d_bbox_head.py	23.23% <0.00%> (ø)
...et3d/models/roi_heads/mask_heads/primitive_head.py	18.91% <ø> (ø)

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[OpenMMLab-Assistant003]

Hi @wHao-Wu！First of all, we want to express our gratitude for your significant PR in the MMDetection3D project. Your contribution is highly appreciated, and we are grateful for your efforts in helping improve this open-source project during your personal time. We believe that many developers will benefit from your PR.

We would also like to invite you to join our Special Interest Group (SIG) private channel on Discord, where you can share your experiences, ideas, and build connections with like-minded peers. To join the SIG channel, simply message moderator— OpenMMLab on Discord or briefly share your open-source contributions in the #introductions channel and we will assist you. Look forward to seeing you there! Join us ：https://discord.gg/raweFPmdzG

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Thank you again for your contribution❤ @wHao-Wu