build!: update library to use Node 12 (#625)

* build!: Update library to use Node 12

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: 2 people

cloud-tasks/package.json

@@ -5,7 +5,7 @@
   "author": "Google Inc.",
   "private": true,
   "engines": {
-    "node": ">=10"
+    "node": ">=12.0.0"
   },
   "files": [
     "*.js"