Don't force mix.combine() to accept an array.

A string with a regular expression would be fine.

src/Verify.js

@@ -55,19 +55,6 @@ class Verify {
     }
 
 
-    /**
-     * Verify that the call the mix.combine() is valid.
-     *
-     * @param {Array} src
-     */
-    static combine(src) {
-        assert(
-            Array.isArray(src),
-            'mix.combine() requires an array as its first parameter.'
-        );
-    }
-
-
     /**
      * Verify that the necessary dependency is available.
      *

src/index.js

@@ -196,8 +196,6 @@ module.exports.preprocess = (type, src, output, pluginOptions) => {
  * @param {string}       output
  */
 module.exports.combine = (src, output) => {
-    Verify.combine(src);
-
     Mix.concat.add({ src, output });
 
     return this;