fix naming

snippets/extend-hex.md

@@ -0,0 +1,10 @@
+### 3-digit hexcode to 6-digit hexcode
+
+Use `Array.map()`, `split()` and `Array.join()` to join the mapped array for converting a three-digit RGB notated hexadecimal color-code to the six-digit form.
+`Array.slice()` is used to remove `#` from string start since it's added once.
+```js
+const extendHex = shortHex =>
+  '#' + shortHex.slice(shortHex.startsWith('#') ? 1 : 0).split().map(x => x+x).join()
+// convertHex('#03f') -> '#0033ff'
+// convertHex('05a') -> '#0055aa'
+```