Fix plotdiagnostics(kf)

[guilhermebodin]

close #311

[codecov]

Codecov Report

Merging #312 (989e7be) into master (4940f7a) will decrease coverage by 2.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #312      +/-   ##
==========================================
- Coverage   93.05%   91.01%   -2.04%     
==========================================
  Files          35       35              
  Lines        3295     3296       +1     
==========================================
- Hits         3066     3000      -66     
- Misses        229      296      +67     

Impacted Files	Coverage Δ
src/kalman_filter_and_smoother.jl	87.85% <0.00%> (-5.61%)	⬇️
src/visualization/diagnostics.jl	0.00% <0.00%> (-98.37%)	⬇️

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