Superscript support for scientific plots (superscript minus and dot operator)

I find that Open Sans works beautifully as a font face for scientific plots (ticks and labels), and I would like to use it as default theme for a scientific visualization library (see [these examples](http://juliaplots.org/AlgebraOfGraphics.jl/dev/generated/penguins/#Frequency-plots)).

The only issue I've encountered so far is that it does not support some characters needed for "log scale plots" to simulate exponents, namely superscript minus `⁻` and dot operator `⋅`.

Compare Open Sans version (using light weight for ticks)


with Fira Sans version (always light weights for ticks)


Would it be possible to add those two glyphs?