fix(deps): update dependency yargs to v12 (#154)

Author: renovate[bot]

samples/package-lock.json

@@ -20,7 +20,7 @@
   "dependencies": {
     "@google-cloud/error-reporting": "^0.5.0",
     "express": "^4.16.3",
-    "yargs": "^11.0.0"
+    "yargs": "^12.0.0"
   },
   "devDependencies": {
     "@google-cloud/nodejs-repo-tools": "^2.3.0",