build: update library to use Node 12 (#729)

* build: Update library to use Node 12

Author: sofisl

compute/package.json

@@ -3,7 +3,7 @@
   "license": "Apache-2.0",
   "author": "Google Inc.",
   "engines": {
-    "node": ">=12"
+    "node": ">=12.0.0"
   },
   "repository": "googleapis/nodejs-compute",
   "private": true,
@@ -26,4 +26,4 @@
     "proxyquire": "^2.0.1",
     "uuid": "^8.0.0"
   }
-}
+}