Fix typo in factorial definition

Author: younishd

wise1617/slides-10.tex

@@ -98,7 +98,7 @@
             n! = \prod\limits_{i=1}^{n} =
                 \begin{cases}
                     n \cdot (n-1)! & \text{if\qquad} x > 0 \\
-                    0 & \text{if\qquad} x = 0
+                    1 & \text{if\qquad} x = 0
                 \end{cases}
             $
         \end{itemize}