format code with gofumpt

Doing a one-pass of formatting the code with gofumpt, which provides a
superset of gofmt.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

osxkeychain/osxkeychain_darwin.go

@@ -8,6 +8,7 @@ package osxkeychain
 #include <stdlib.h>
 */
 import "C"
+
 import (
 	"errors"
 	"strconv"