Add slugify example

Author: imteekay

javascript/immutability/slugify.js

@@ -0,0 +1,14 @@
+const mutationWithSlugify = (string) => {
+  string = string.toLowerCase(); 
+  string = string.trim(); 
+  string = string.split(' '); 
+  string = string.join('-');
+  return string;
+}
+
+const slugify = (string) =>
+  string
+    .toLowerCase()
+    .trim()
+    .split(' ')
+    .join('-');