Fix section 3.1.8 URI

README.md

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 ### Part 3.1.8 - Test
 * Restart the QuickPoll application.
-* Use Postman to execute a `POST` to `http://localhost:8080/polls/1` whose request body is the `JSON` object below.
+* Use Postman to execute a `POST` to `http://localhost:8080/polls/` whose request body is the `JSON` object below.
 * You can modify the request body in Postman by navigating to the `Body` tab, selecting the `raw` radio button, and selecting the `JSON` option from the text format dropdown.
 
 ```JSON