Remove array-flatten dependency

lib/operation.js

@@ -1,6 +1,5 @@
 'use strict';
 
-const { flatten: flattenArray } = require('array-flatten');
 const color = require('color');
 const is = require('./is');
 
@@ -127,7 +126,7 @@ function flop (flop) {
  * @throws {Error} Invalid parameters
  */
 function affine (matrix, options) {
-  const flatMatrix = flattenArray(matrix);
+  const flatMatrix = [].concat(...matrix);
   if (flatMatrix.length === 4 && flatMatrix.every(is.number)) {
     this.options.affineMatrix = flatMatrix;
   } else {