Bugfix. KdocMethod should not raise warning on override fun

[aktsay6]

What's done:

• Fixed bugs

This pull request closes #551

[codecov]

Codecov Report

Merging #594 (21b7f90) into master (2349037) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #594   +/-   ##
=========================================
  Coverage     80.84%   80.84%           
- Complexity     1704     1705    +1     
=========================================
  Files            87       87           
  Lines          4365     4365           
  Branches       1346     1346           
=========================================
  Hits           3529     3529           
  Misses          297      297           
  Partials        539      539           

Flag	Coverage Δ	Complexity Δ
unittests	80.84% <100.00%> (ø)	0.00 <0.00> (ø)

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Impacted Files	Coverage Δ	Complexity Δ
.../org/cqfn/diktat/ruleset/rules/kdoc/KdocMethods.kt	90.19% <100.00%> (ø)	70.00 <0.00> (+1.00)

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