Remove explicit new line addition

This removes instances of `\n` in the function calls for `append_to_zshrc`.
The function will only handle literal strings.

Relies on `append_to_zshrc` to add a new line after the appended text.

`append_to_zshrc()` will accept a second argument (`boolean`) to skip the new
line before the appended text, by default a new line will always be prepended.