fix(deps): update dependency @grpc/grpc-js to ~1.6.0 (GoogleCloudPlatform#143)

Author: renovate-bot

package.json

@@ -32,7 +32,7 @@
     "node": ">=8"
   },
   "dependencies": {
-    "@grpc/grpc-js": "~1.5.0"
+    "@grpc/grpc-js": "~1.6.0"
   },
   "devDependencies": {
     "@grpc/proto-loader": "^0.6.2",