Update to use Go modules

Fixes: #109

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

vendor/github.com/sirupsen/logrus/terminal_check_solaris.go

@@ -0,0 +1,11 @@
+package logrus
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+// IsTerminal returns true if the given file descriptor is a terminal.
+func isTerminal(fd int) bool {
+	_, err := unix.IoctlGetTermio(fd, unix.TCGETA)
+	return err == nil
+}