Better text color selection for a given background

[kosumosu]

Currently, apexcharts selects text color inadequately. It can select white text for quiet bright background.
The problem is that computeTextColor() function uses linear colorObj.getLuminance(), which is not how human percepts color.
TinyColor has isLight()/isDark() methods, which work in gamma space, and my experiments indicate it works better for this purpose.
Here is the comparison (before/after):

The color of the graph is #BAACC7 which has linear luminance of about 0.44. This is less than 0.5, thus master version of apex-charts selects white text color. However, as you can probably see, black text color is much more readable.