Add testing agains each feat PT version

[Borda]

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• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

What does this PR do?

Fixes #125

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[codecov]

Codecov Report

Merging #127 (042c191) into master (2601642) will decrease coverage by 0.37%.
The diff coverage is 72.72%.

@@            Coverage Diff             @@
##           master     #127      +/-   ##
==========================================
- Coverage   96.61%   96.24%   -0.38%     
==========================================
  Files         140       70      -70     
  Lines        4376     2210    -2166     
==========================================
- Hits         4228     2127    -2101     
+ Misses        148       83      -65     

Flag	Coverage Δ
Linux	78.77% <72.72%> (-0.07%)	⬇️
Windows	78.77% <72.72%> (-0.07%)	⬇️
cpu	96.24% <72.72%> (-0.24%)	⬇️
gpu	?
macOS	96.24% <72.72%> (-0.24%)	⬇️
pytest	96.24% <72.72%> (-0.38%)	⬇️
python3.6	96.23% <72.72%> (-0.24%)	⬇️
python3.8	96.24% <72.72%> (-0.24%)	⬇️
python3.9	96.24% <72.72%> (-0.24%)	⬇️
torch1.3.1	94.96% <72.72%> (-0.23%)	⬇️
torch1.4.0	95.11% <72.72%> (-0.23%)	⬇️
torch1.8.1	96.24% <72.72%> (-0.24%)	⬇️

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

Impacted Files	Coverage Δ
torchmetrics/utilities/imports.py	77.77% <72.72%> (-22.23%)	⬇️
__w/1/s/torchmetrics/utilities/__init__.py
__w/1/s/torchmetrics/classification/roc.py
...s/torchmetrics/classification/matthews_corrcoef.py
...etrics/functional/regression/explained_variance.py
...hmetrics/functional/retrieval/average_precision.py
...s/torchmetrics/classification/average_precision.py
__w/1/s/torchmetrics/classification/checks.py
...torchmetrics/functional/classification/__init__.py
__w/1/s/torchmetrics/classification/__init__.py
... and 61 more

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[pep8speaks]

Hello @Borda! Thanks for updating this PR.

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-03-25 19:17:17 UTC

[tchaton]

LGTM !