Update RFC-00xx-special-functions.md

Author: 0x00b1

RFC-00xx-special-functions.md

@@ -1434,7 +1434,7 @@ $$J_{n}(z)=\sum _{k=0}^{\infty } \frac{(-1)^k \left(\frac{z}{2}\right)^{2k+n}}{\
 
 where $\Gamma$ is the gamma function.
 
-$J_{n}(z)$ is defined for $\left\\{n \in \mathbb{Z}, z \in \mathbb{R} \right\\}$, 
+$J_{n}(z)$ is defined for $\left\\{n \in \mathbb{Z}, z \in \mathbb{R} \right\\}$, $\left\\{n \in \mathbb{Z}, z \in \mathbb{C} \right\\}$, 
 
 ##### Parameters