fix: Add missing dependency underscore.

Author: thet

package.json

@@ -5,7 +5,8 @@
     "license": "MIT",
     "main": "./src/pat-content-mirror.js",
     "dependencies": {
-        "@patternslib/patternslib": "^6.0.1"
+        "@patternslib/patternslib": "^6.0.1",
+        "underscore": "^1.13.2"
     },
     "devDependencies": {
         "@babel/core": "^7.16.0",