V3: [Go] Use consistent formatting for output in examples

[ErikSchierboom]

Looking at the existing Go exercises, there is some inconsistency regarding the format used to show the result of calling a function in examples found in instructions.md files. I've found the following variants:

• // Output: X
• // => X
• // Returns: X

It would be good to standardize on one format. I have no preference, while noting that there are a couple of tracks that use =>. But it should use what makes sense most for Go.

[oanaOM]

I can look into this and make it consistent across all exercises.

[oanaOM]

I made the changes and it should be consistent across all exercises.

[ErikSchierboom]

Great!