Add "Tail Swap" kata

Author: juan-antonio-ledesma

7-kyu/tail-swap.md

@@ -0,0 +1,31 @@
+<h1>Tail Swap <sup><sup>7 Kyu</sup></sup></h1>
+
+<sup>
+  <a href="https://www.codewars.com/kata/5868812b15f0057e05000001">
+    <strong>LINK TO THE KATA</strong>
+  </a> - <code>FUNDAMENTALS</code>
+</sup>
+
+## Description
+
+You'll be given a list of two strings, and each will contain exactly one colon (`":"`) in the middle (but not at beginning or end). The length of the strings, before and after the colon, are random.
+
+Your job is to return a list of two strings (in the same order as the original list), but with the characters after each colon swapped.
+
+**Examples**
+
+```
+["abc:123", "cde:456"]  -->  ["abc:456", "cde:123"]
+["a:12345", "777:xyz"]  -->  ["a:xyz", "777:12345"]
+```
+
+## Solution
+
+```javascript
+const tailSwap = arr => {
+  const pair1 = arr[0].split(':')
+  const pair2 = arr[1].split(':')
+
+  return [`${pair1[0]}:${pair2[1]}`, `${pair2[0]}:${pair1[1]}`]
+}ddBinary = (a, b) => (a + b).toString(2)
+```

README.md

@@ -218,6 +218,7 @@ JavaScript katas on Codewars are programming challenges that help you improve yo
 - **[Sum of odd numbers](./7-kyu/sum-of-odd-numbers.md)**<br><sup>`ARRAYS` `LISTS` `MATHEMATICS` `FUNDAMENTALS`</sup>
 - **[Sum of the first nth term of Series](./7-kyu/sum-of-the-first-nth-term-of-series.md)**<br><sup>`FUNDAMENTALS`</sup>
 - **[Sum of two lowest positive integers](./7-kyu/sum-of-two-lowest-positive-integers.md)**<br><sup>`ARRAYS` `FUNDAMENTALS`</sup>
+- **[Tail Swap](./7-kyu/tail-swap.md)**<br><sup>`FUNDAMENTALS`</sup>
 - **[Testing 1-2-3](./7-kyu/testing-1-2-3.md)**<br><sup>`ARRAYS` `FUNDAMENTALS`</sup>
 - **[The highest profit wins!](./7-kyu/the-highest-profit-wins.md)**<br><sup>`LISTS` `ARRAYS` `FUNDAMENTALS`</sup>
 - **[The Office I - Outed](./7-kyu/the-office-i-outed.md)**<br><sup>`FUNDAMENTALS` `ARRAYS`</sup>