Update your golang_refcard.pdf, please

outer_var in the outer func wasn't changed because the anonymous inner function hadn't been called yet.
```go
// Closures: don't mutate outer vars, instead redefine them!
func outer() (func() int, int) {
outer_var := 2 // NOTE outer_var is outside inner's scope
inner := func() int {
outer_var += 99 // attempt to mutate outer_var
return outer_var // => 101 (but outer_var is a newly redefined
// variable visible only inside inner)
}
return inner, outer_var // => 101, 2 (still!)
}
```
I saw you made updates on the README file, but some people may also read your pdf file.

The issue points to a discrepancy between the README and the PDF version of the cheat sheet. Locate the PDF file (likely named golang_refcard.pdf) in the repository, find the section on closures, and update the example to match the corrected version from the README. Verify the change by opening the PDF to ensure the example correctly shows that outer_var is not mutated until the inner function is called.

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