Fix example rendering in Mahalanobis docs

[navidcy]

No description provided.

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -5.82 ⚠️

Comparison is base (b8cddf2) 95.27% compared to head (dc11505) 89.45%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #254      +/-   ##
==========================================
- Coverage   95.27%   89.45%   -5.82%     
==========================================
  Files           9        9              
  Lines         867      531     -336     
==========================================
- Hits          826      475     -351     
- Misses         41       56      +15     

Impacted Files	Coverage Δ
src/mahalanobis.jl	92.50% <ø> (-6.24%)	⬇️

... and 8 files with indirect coverage changes

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