doc: synopsis-docs match Hello, World! in program and console output.

doc/api/synopsis.md

@@ -10,7 +10,7 @@ different options and ways to run scripts with Node.js.
 
 ## Example
 An example of a [web server][] written with Node.js which responds with
-`'Hello World!'`:
+`'Hello, World!'`:
 
 Commands displayed in this document are shown starting with `$` or `>`
 to replicate how they would appear in a user's terminal.
@@ -71,7 +71,7 @@ const port = 3000;
 const server = http.createServer((req, res) => {
   res.statusCode = 200;
   res.setHeader('Content-Type', 'text/plain');
-  res.end('Hello World!\n');
+  res.end('Hello, World!\n');
 });
 
 server.listen(port, hostname, () => {
@@ -94,7 +94,7 @@ Server running at http://127.0.0.1:3000/
 
 Now, open any preferred web browser and visit `http://127.0.0.1:3000`.
 
-If the browser displays the string `Hello, world!`, that indicates
+If the browser displays the string `Hello, World!`, that indicates
 the server is working.
 
 Many of the examples in the documentation can be run similarly.