Bayesian A/B testing: slight changes to math

Using pandoc, you can build it something like this:

```
# First step, md to tex
# Custom preamble can be applied her (remove the --standalone option)
pandoc -f markdown --latex-engine=lualatex -R --standalone -i text.md -o text.tex
# Second step md to pdf
lualatex --output-directory=build text.tex
```