fix: Use proper method for checking is object an array (#8644)

Author: tykus160

lib/text/cue.js

@@ -350,7 +350,7 @@ shaka.text.Cue = class {
       // Make copies of array fields, but only one level deep.  That way, if we
       // change, for instance, textDecoration on the clone, we don't affect the
       // original.
-      if (clone[k] && clone[k].constructor == Array) {
+      if (Array.isArray(clone[k])) {
         clone[k] = /** @type {!Array} */(clone[k]).slice();
       }
     }

lib/util/object_utils.js

@@ -54,7 +54,7 @@ shaka.util.ObjectUtils = class {
             return null;
           }
 
-          const isArray = val.constructor == Array;
+          const isArray = Array.isArray(val);
           if (val.constructor != Object && !isArray) {
             return null;
           }