Fix typos in training.md

[JingchaoZhang]

another typo.

[codecov-commenter]

Codecov Report

Merging #1238 (08a6936) into devel (d477507) will decrease coverage by 11.81%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##            devel    #1238       +/-   ##
===========================================
- Coverage   76.10%   64.28%   -11.82%     
===========================================
  Files          91        5       -86     
  Lines        7302       14     -7288     
===========================================
- Hits         5557        9     -5548     
+ Misses       1745        5     -1740     

Impacted Files	Coverage Δ
deepmd/descriptor/se_a.py
deepmd/utils/argcheck.py
deepmd/descriptor/hybrid.py
deepmd/utils/convert.py
deepmd/fit/wfc.py
deepmd/train/run_options.py
deepmd/utils/tabulate.py
deepmd/utils/weight_avg.py
deepmd/utils/plugin.py
deepmd/loss/ener.py
... and 76 more

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