merge: improve median (TheAlgorithms#869)

* median

* [TheAlgorithms/pull/869] make fn pure

* [TheAlgorithms/pull/869/] pure averageMedian fn

* [TheAlgorithms/pull/869] formatter

Author: RuSaG0

Maths/AverageMedian.js

@@ -8,7 +8,8 @@
  * else if the length of the array is odd number, the median value will be the middle number in the array
  */
 
-const averageMedian = (numbers) => {
+const averageMedian = (sourceArrayOfNumbers) => {
+  let numbers = [...sourceArrayOfNumbers]
   let median = 0
   const numLength = numbers.length
   numbers = numbers.sort(sortNumbers)