Fix the AppEngine deployment runtime as NodeJS

The app.yaml should use nodejs as runtime for React application. The python runtime will cause the deployment failure. The PR suggests using nodejs18 as stable Nodejs runtime.

Author: gangchen03

demos/palm/web/travel-planner/app.yaml

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-runtime: python310
+runtime: nodejs18
 
 handlers:
 - url: /