Update _classification.py

[themrzmaster]

Reference Issue

What does this implement/fix? Explain your changes.

fix caption and specificity definition.

Any other comments?

[chkoar]

Good catch thanks.

[codecov]

Codecov Report

Merging #592 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #592      +/-   ##
==========================================
+ Coverage   98.92%   98.93%   +<.01%     
==========================================
  Files          85       85              
  Lines        5324     5336      +12     
==========================================
+ Hits         5267     5279      +12     
  Misses         57       57

Impacted Files	Coverage Δ
imblearn/metrics/_classification.py	95.65% <ø> (ø)	⬆️
imblearn/utils/tests/test_show_versions.py	100% <0%> (ø)	⬆️
imblearn/utils/_show_versions.py	100% <0%> (ø)	⬆️

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