challenge_fetcher: Newline replacements are a bit wonky

[NathanielJS1541]

The README files sometimes don't properly mimic the Project Euler pages due to the placement (or lack thereof) of newlines. An example would be the markdown for problem 39, which does not have newlines around the following LaTeX expression:
${20,48,52}$, ${24,45,51}$, ${30,40,50}$

[NathanielJS1541]

Newline replacements are now fixed, but the test against Challenge 39 is still failing due to bad escaping of the curly braces {} in the output. This prevents the LaTeX from rendering correctly.

This is the current output:

$\{20,48,52\}$, $\{24,45,51\}$, $\{30,40,50\}$

Which renders as follows:
${20,48,52}$, ${24,45,51}$, ${30,40,50}$

Escaped correctly it should be this:

$\\{20,48,52\\}$, $\\{24,45,51\\}$, $\\{30,40,50\\}$

Which renders like this:
$\{20,48,52\}$, $\{24,45,51\}$, $\{30,40,50\}$