Update unist-util-is

Author: wooorm

package.json

@@ -22,7 +22,7 @@
     "Titus Wormer <[email protected]> (https://wooorm.com)"
   ],
   "dependencies": {
-    "unist-util-is": "^3.0.0"
+    "unist-util-is": "^4.0.0"
   },
   "devDependencies": {
     "browserify": "^16.0.0",