Super minor typo fix (#893)

functions.Rmd

@@ -150,7 +150,7 @@ This is an important part of the "do not repeat yourself" (or DRY) principle. Th
     sd(x, na.rm = TRUE) / mean(x, na.rm = TRUE)
     ```
 
-1.  write your own functions to compute the variance and skewness of a numeric vector.
+1.  Write your own functions to compute the variance and skewness of a numeric vector.
     Variance is defined as
     $$
     \mathrm{Var}(x) = \frac{1}{n - 1} \sum_{i=1}^n (x_i - \bar{x}) ^2 \text{,}