cmd/go: gofmt should ignore vendor

[abhigenie92]

When you run go fmt $$(go list ./...) it ignores vendor by default but gofmt . doesn't do that.
The use case is if you run fmt without the code modification in-place and ignore the vendor.

One way is gofmt -l (find . -type f -name '*.go'| grep -v "/vendor/"), is there an easier way?

[katiehockman]

/cc @bcmills @jayconrod

[bcmills]

@abhigenie92, please fill out the full issue template — specifically, it would be helpful to know the exact commands you ran that led to confusion, and to clarify what you observed vs. what you expected.

Specifically:

• What concrete problem were you trying to solve that led you to run gofmt .?
• Did you actively cd into the vendor directory before running the command?
• Are you talking about the behavior of go fmt ., or gofmt .? (That is, is this the problem found in cmd/go, cmd/gofmt, or both?) How did you choose between them?

[bcmills]

See also #29751.

[gopherbot]

Timed out in state WaitingForInfo. Closing.

(I am just a bot, though. Please speak up if this is a mistake or you have the requested information.)