chartjs config tweaked

[euanwm]

Weird issue found was likely a Brave browser issue. Tested against Firefox and the issue wasn't present. Tweaked the ChartJS options anyway so that it fits as close to the original without type errors.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.25%. Comparing base (bb120f4) to head (1cbd23b).
Report is 2 commits behind head on development.

Additional details and impacted files

@@             Coverage Diff              @@
##           development     #407   +/-   ##
============================================
  Coverage        69.25%   69.25%           
============================================
  Files               18       18           
  Lines              605      605           
  Branches             5        5           
============================================
  Hits               419      419           
  Misses             173      173           
  Partials            13       13           

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