chore(deps): update dependency duplexify to v4 (#539)

Author: renovate[bot]

handwritten/firestore/package.json

@@ -72,7 +72,7 @@
     "chai": "^4.1.2",
     "chai-as-promised": "^7.1.1",
     "codecov": "^3.0.2",
-    "duplexify": "^3.6.0",
+    "duplexify": "^4.0.0",
     "gts": "^0.9.0",
     "hard-rejection": "^1.0.0",
     "jsdoc-baseline": "git+https://github.com/hegemonic/jsdoc-baseline.git",