Run gofmt/goimports even if goreturn cannot build the package

[zimmski]

1. Put the following into "$GOPATH/src/sourcegraph.com/sqs/goreturns/hey/ho.go"

// +build something

package main

func foo() { }

2. Execute goreturns -d $GOPATH/src/sourcegraph.com/sqs/goreturns/hey/ho.go

The execution will print the problem "no buildable Go source files in ...".

I am not saying that goreturns should automatically interpret the build tags and then build the package with the correct tags, but it would be nice if it could run gofmt/goimports anyway.

[sqs]

Thanks. Good call. I'd happily accept a PR that implements this.