fix(deps): update dependency yargs to v14 (#680)

Author: renovate-bot

package.json

@@ -119,6 +119,6 @@
     "time-span": "^3.0.0",
     "typescript": "~3.4.0",
     "uuid": "^3.3.2",
-    "yargs": "^13.0.0"
+    "yargs": "^14.0.0"
   }
 }

samples/package.json

@@ -15,7 +15,7 @@
   },
   "dependencies": {
     "@google-cloud/spanner": "^4.0.2",
-    "yargs": "^13.0.0"
+    "yargs": "^14.0.0"
   },
   "devDependencies": {
     "chai": "^4.2.0",