Okay, it's done. Pkg.update(); Pkg.add("LaTeXStrings") to get it.
Note also that in the new version you don't have to type the $...$ if your
string contains only an equation; they are added automatically if no
unescaped dollar sign is found. (The only point of using this is for
equations, since IJulia ignores other LaTeX formatting commands; you can
use the LaTeXString(s) constructor if you really need a text/latex string
with no equations.) I got tired of continually forgetting to type $...$
in my plot labels.
