Typo in docs for qmutilde test-statistic

[andrewfowlie]

Minor typo, though worth fixing

pyhf/src/pyhf/infer/test_statistics.py

Lines 174 to 180 in 5b63251

	\begin{equation}
	\tilde{\lambda}\left(\mu\right) = \left\{\begin{array}{ll}
	\frac{L\left(\mu, \hat{\hat{\boldsymbol{\theta}}}(\mu)\right)}{L\left(\hat{\mu}, \hat{\hat{\boldsymbol{\theta}}}(0)\right)}, &\hat{\mu} < 0,\\
	\frac{L\left(\mu, \hat{\hat{\boldsymbol{\theta}}}(\mu)\right)}{L\left(\hat{\mu}, \hat{\boldsymbol{\theta}}\right)}, &\hat{\mu} \geq 0.
	\end{array}\right.
	\end{equation}

On L176, I think a \hat{\mu} should be replaced by 0. This is in the denominator of the \hat{\mu} < 0 case. It's easier to read in the latex rendered docs

https://scikit-hep.org/pyhf/_generated/pyhf.infer.test_statistics.qmu_tilde.html#pyhf.infer.test_statistics.qmu_tilde

[andrewfowlie]

Would it help if I made a PR for this?