refactor: simplify flatten function using Array.prototype.flat

Author: dvd101x

src/utils/array.js

@@ -472,17 +472,7 @@ export function flatten (array) {
     // if not an array, return as is
     return array
   }
-  const flat = []
-
-  array.forEach(function callback (value) {
-    if (Array.isArray(value)) {
-      value.forEach(callback) // traverse through sub-arrays recursively
-    } else {
-      flat.push(value)
-    }
-  })
-
-  return flat
+  return array.flat(Infinity)
 }
 
 /**