[BUG] In ReadTheDocs, math expression rendering error with ʃ

[stannam]

Describe the bug

The documentation is hard to read as some mathematical expressions are not rendered. https://corpustools.readthedocs.io/en/latest/mutual_information.html

I think the ʃ symbol is the cause.

CorpusTools/docs/source/mutual_information.rst

Lines 164 to 170 in 36868d7

	Let's first calculate pMI(ʃ,i) without environment filtering as the baseline. Using the numbers presented
	in the table,
	:math:`pMI (ʃ,i) = log_2 (\frac{p(ʃi)}
	{p(ʃ)*p(i)}) = 2.28`
	since, :math:`p(ʃi) = \frac{3}{17}`, :math:`p(ʃ) = \frac{4}{21}`, and :math:`p(i) = \frac{4}{21}`