fix(deps): update dependency through2 to v3 (#359)

Author: renovate[bot]

handwritten/bigtable/package.json

@@ -82,7 +82,7 @@
     "retry-request": "^4.0.0",
     "stream-events": "^1.0.2",
     "string-format-obj": "^1.0.0",
-    "through2": "^2.0.3"
+    "through2": "^3.0.0"
   },
   "devDependencies": {
     "@google-cloud/nodejs-repo-tools": "^2.2.3",