See how Boundary would look with gofumpt applied (#853)

* See how Boundary would look with https://github.com/mvdan/gofumpt applied

Results of running `gofumpt -w -s .`

* Update tools file and Makefile for gofumpt

Co-authored-by: Jeff Mitchell <jeffrey.mitchell@gmail.com>

api/output_string.go

@@ -12,9 +12,7 @@ const (
 	ErrOutputStringRequest = "output a string, please"
 )
 
-var (
-	LastOutputStringError *OutputStringError
-)
+var LastOutputStringError *OutputStringError
 
 type OutputStringError struct {
 	*retryablehttp.Request