fix invalid escape sequence

Author: MikaelSlevinsky

src/specialfunctions.jl

@@ -179,9 +179,9 @@ unsafe_gamma(z) = gamma(z)
 """
     @lanczosratio(z, ϵ, c₀, c...)
 
-Evaluate ``\\dfrac{\\sum_{k=0}^{N-1} \\frac{c[k+1]}{(z+k)(z+k+ϵ)}}{c₀ + \\sum_{k=0}^{N-1} \\frac{c[k+1]}{z+k}}`.
+Evaluate ``\\dfrac{\\sum_{k=0}^{N-1} \\frac{c[k+1]}{(z+k)(z+k+\\epsilon)}}{c\_0 + \\sum_{k=0}^{N-1} \\frac{c[k+1]}{z+k}}`.
 
-This ratio is used in the Lanczos approximation of ``\log\\frac{\\Gamma(z+\\epsilon)}{\\Gamma(z)}`` in
+This ratio is used in the Lanczos approximation of ``\\log\\frac{\\Gamma(z+\\epsilon)}{\\Gamma(z)}`` in
 
 > N. Michel and M. V. Stoitsov, [Fast computation of the Gauss hypergeometric function with all its parameters complex with application to the Pöschl–Teller–Ginocchio potential wave functions](https://doi.org/10.1016/j.cpc.2007.11.007), Comp. Phys. Commun., 178:535–551, 2008.
 """