Invalid tex in regression lecture (and others?) #181

The regression lecture is using unescaped latex in a name. This seems to work in the html renderer, but not in the katex one used in vscode jupyter notebooks.

That is,

$$
\log(\text{price}) = \beta_0 + \beta_1 \text{sqft_living} + \epsilon
$$

is incorrect and should be

$$
\log(\text{price}) = \beta_0 + \beta_1 \text{sqft\_living} + \epsilon
$$

or something similar.

We should look to see if there are other locations that could have this issue.