flag: changed flag variable name in package doc, for clarity
flag: changed flag variable name in package doc, for clarity

Changed the flag variable name to nFlag instead of flagname,
because flagname was confusing.

Change-Id: I20dd4c4b4f605395d427a125ba4fd14580e5d766
Reviewed-on: https://go-review.googlesource.com/c/go/+/221678
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

akutz/go,akutz/go,akutz/go,CAFxX/go,golang/go,golang/go,cloudflare/go,nawawi/go,nawawi/go,CAFxX/go,cloudflare/go,golang/go,nawawi/go,akutz/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,cloudflare/go,golang/go,CAFxX/go,nawawi/go,akutz/go,cloudflare/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,cloudflare/go,golang/go,akutz/go,nawawi/go,golang/go,CAFxX/go,akutz/go,CAFxX/go,akutz/go,cloudflare/go,golang/go,CAFxX/go