Fix mistakes in formula

[likaixin2000]

Missing newlines cause a wrong rendering of the formulas.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #8607 (42eecc8) into master (3b72b12) will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #8607      +/-   ##
==========================================
- Coverage   64.17%   64.02%   -0.16%     
==========================================
  Files         361      361              
  Lines       29530    29525       -5     
  Branches     5020     5020              
==========================================
- Hits        18951    18902      -49     
- Misses       9576     9610      +34     
- Partials     1003     1013      +10     

Flag	Coverage Δ
unittests	64.02% <ø> (-0.14%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmdet/models/utils/gaussian_target.py	93.93% <ø> (ø)
mmdet/utils/setup_env.py	68.00% <0.00%> (-24.00%)	⬇️
mmdet/datasets/builder.py	45.83% <0.00%> (-7.30%)	⬇️
mmdet/core/bbox/assigners/sim_ota_assigner.py	80.00% <0.00%> (-3.64%)	⬇️
mmdet/utils/misc.py	61.53% <0.00%> (-2.57%)	⬇️
mmdet/models/dense_heads/dense_test_mixins.py	40.74% <0.00%> (-2.47%)	⬇️
mmdet/models/roi_heads/test_mixins.py	50.71% <0.00%> (-2.15%)	⬇️
mmdet/datasets/pipelines/transforms.py	74.19% <0.00%> (-1.81%)	⬇️
mmdet/core/bbox/assigners/max_iou_assigner.py	72.36% <0.00%> (-1.32%)	⬇️
mmdet/datasets/custom.py	61.25% <0.00%> (-0.21%)	⬇️
... and 1 more

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[BIGWangYuDong]

This PR should be merged into the dev branch.