Refactor: shorten bolts name

[Borda]

What does this PR do?

make the name consistent with all other PL packages
needed after real rename:

• rename Read-the-Docs - Communicate the project slug can be changed by requesting it readthedocs/readthedocs.org#5403

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[codecov]

Codecov Report

Merging #583 (d48580e) into master (79d4184) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #583      +/-   ##
==========================================
- Coverage   76.58%   76.54%   -0.05%     
==========================================
  Files         117      117              
  Lines        6850     6850              
==========================================
- Hits         5246     5243       -3     
- Misses       1604     1607       +3     

Flag	Coverage Δ
cpu	26.20% <100.00%> (ø)
pytest	26.20% <100.00%> (ø)
unittests	76.02% <100.00%> (-0.05%)	⬇️

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

Impacted Files	Coverage Δ
pl_bolts/__init__.py	90.47% <100.00%> (ø)
...l_bolts/models/rl/vanilla_policy_gradient_model.py	92.79% <0.00%> (-2.71%)	⬇️

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[tchaton]

LGTM !