build!: update library to use Node 12 (#539)

* build!: Update library to use Node 12

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

Author: sofisl

container/snippets/package.json

@@ -3,7 +3,7 @@
   "license": "Apache-2.0",
   "author": "Google Inc.",
   "engines": {
-    "node": ">=10"
+    "node": ">=12.0.0"
   },
   "repository": "googleapis/nodejs-cloud-container",
   "private": true,