fix naming

snippets/average.md

@@ -0,0 +1,8 @@
+### Average of array of numbers
+
+Use `Array.reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
+
+```js
+const average = arr => arr.reduce((acc, val) => acc + val, 0) / arr.length;
+// average([1,2,3]) -> 2
+```