Updating $provide.service method docs

[clark-pan]

The previous example provided for the service method did not work. I've updated the example to a working example.

[mary-poppins]

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[clark-pan]

Bump. Signed CLA

[mary-poppins]

CLA signature verified! Thank you!

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[caitp]

Hey, so the example in the docs is returning the constructor for the Ping "class", the example doesn't really reflect that and would need to show it used as

var pinger = new ping();
pinger.send();

Or just having the service return new Ping();, this would be a much smaller change... But yeah I guess your version is probably the one that would make sense to people.