tutorial: omit hostname from router.Run in web-service-gin

[tyrellcurry]

Update the web-service-gin tutorial to call router.Run(":8080")
instead of router.Run("localhost:8080"). Binding to localhost
prevents the tutorial from working in environments where the
client and server are not on the same loopback interface, such
as Google Cloud Shell, where following the tutorial verbatim
produces:

$ curl http://localhost:8080/albums
curl: (7) Failed to connect to localhost port 8080 after
0 ms: Couldn't connect to server

Omitting the hostname binds to all available interfaces and
matches the convention used in Gin's own documentation, letting
the curl command in the tutorial succeed in these environments.

Fixes golang/go#80944

[gopherbot]

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Tyrell Curry:

Patch Set 1:

(2 comments)

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[gopherbot]

Message from Tyrell Curry:

Patch Set 3: Code-Review+1

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